Two years later…

Olivia and John walked into Warner's office after receiving a call about their DNA sample that they found buy their victim.

"Get a hit?" Olivia asked as she spotted the doctor.

"No, but we did match it to his Y-chromosome and we found someone in the system" Melinda answered as she pulled out a file from a shelf.

"His son?" Olivia questioned.

"Like father like son" John chimed in.

Melinda smirked and shook her head "Not at all John. I found it rather weird knowing the history behind this guy so I called the doctor that has his DNA sample and I ran it myself and it matches."

John and Olivia both had the confused look on their faces not sure what was going on. "Wait…so his son is in the system?" John asked.

"Not that system." Melinda answered as she opened the file in her hands and kept it to her chest "He is a Fed" She looked over at Olivia "I don't think you will have trouble finding him" She slowly handed the file to Olivia "Mark was the hit for the Y-chromosome"

Olivia's mouth dropped looking at Mark's NYPD and FBI file "No. There has to be a mistake, Mark's father died when Mark was five. It's a mistake"

"It's not. I ran the DNA sample at the crime scene two times and then ran Mark's and it matches. I wanted to make sure so I found James's DNA in the school system and all Y-chromosomes match. You're looking for Mark's father"

John and Olivia looked over at each other and then back at Mark's file. Olivia just looked at her husband's picture that was clipped to the file. She shook her head again. "It can't be"

"Maybe it's like an uncle or something," John offered.

"His mother and father were an only child, he doesn't have any family"

"There is another explanation for it" Melinda spoke up.

Olivia looked up at her quickly "What?"

"Mark's father committed suicide and then killed his mother right?"

"Yea" Olivia answered with a nod.

"What if that man wasn't his father?"

"What are you talking about? His father was a FBI agent, Marcus Anderson; he should be in the system"

"He is" Melinda answered with a nod "But he wasn't Mark's father, I ran Mark's DNA and then looked up Marcus Anderson and looked over his files and their Y-chromosomes don't match. Lilly Anderson was in the system as well after her death and part of her DNA does match Mark's"

"His mother had an affair" John figured out "Mark is the product of that affair.

Olivia closed her eyes trying to suppress her tears "You can't let Mark know this"

Melinda and John looked at her at the same time.

"He would want to know that his real father is still alive wouldn't he?" John asked.

"He will think it was his fault for the murder-suicide. This information doesn't leave this office you understand me?"

Melinda and John both nodded knowing that Olivia knew him the best.

Olivia got home later that night and went straight to her room and to her panty drawer since Mark kept the keys to his drawer in there. He always joked that he wanted a reason to touch her panties and not seem rude so after a while Olivia playfully put the keys in there.

She opened his drawer where he kept his gun and badge and some files from work. She took out the stack of files and started to look through them to find the Anderson case file she knew was in there.

"Mommy"

She got startled and turned around and spotted Mike standing in the doorway "Yea sweetie?"

"I want some ice cream"

"Give me a second honey. Go in the kitchen, I'll meet you there ok?"

"Ok" Mike nodded and did what he was told.

Olivia kept flipping through the files and the pictures of the victims and the suspects were getting worse by the picture. She never understood how he was able to have a great sense of humor after everything he saw everyday but she loved him for not bringing his work home or to his family. "C'mon" She mumbled to herself since she was trying to go fast and get the file before Mark got home from work.

She went through all of them and still didn't spot the one she needed. She took a deep breath as she put her hair behind her ears. She spotted two files under his extra gun he kept home and hardly ever brought to work.

Olivia moved the gun out of the way and pulled out both files. She opened one and nodded seeing the Anderson file there. She put it to the side and out of curiosity took the other file wondering why he kept it away from the other ones from work.

She opened it and looked over the name and found out it was her mother's case. She took a deep breath seeing all the notes he made and officer's names he had written down. She smiled a little realizing he was working on her mother's case even with the huge caseload he had at work.

"Mommy c'mon" Mike whined from the kitchen.

Olivia put all the files back in the drawer except for the Anderson one and locked the drawer.

She put the file under her pillow and finally took off her jacket since she didn't even do that in how much of a hurry she was.

She went to the kitchen where now Mike, Matt and Lilly were all there waiting for her. "All of you guys want ice cream?"

All three nodded. Olivia smiled and gave them each a kiss on the head and took the ice cream out of the freezer.

"Put fudge on it" Matt demanded looking up at her as Olivia started putting Ice Cream in bowls for them.

"And frosting" Mike added.

"And Ceweal" Lilly yelled out as she hugged Olivia around the leg.

Olivia looked down at her "Did daddy teach you about the cereal on ice cream?"

She smiled and nodded "Yea"

"That's what I thought" Olivia smirked. "Who wants the blue spoon?"

"Me" Mike and Lilly yelled out at the same time.

"I'm older" Mike gave her a look.

"I'm a giwl" Lilly returned the same look.

"I want blue, I want blue" Mark yelled out coming into the kitchen with files in his hand.

"Daddy!" All three kids yelled out at the same time.

"Children!" He yelled back and put his files down on the table and took off his blazer. "Who wants to fly?"

All three raised their hands.

"Well I don't know…hmm..." Mark kneeled down "Who gives me a cooler kiss goes first"

Lilly ran over to him first and wrapped her small arms around his neck and gave him a kiss on the cheek "I love you daddy"

"Aww I love you too sweetie" he gave her a kiss. "Sorry boys but your sister wins because she is a girl" Mark picked Lilly up and flied her around the room.

"Daddy" Matt whined.

"Ladies first boys," Mark put Lilly back on the ground "If you went first and a lady should have then you're a girl"

Mike and Matt nodded.

"Mike who gets the blue spoon?" Mark questioned.

Olivia just smiled since Mark thought James the same way how to be a gentleman.

"Lilly" Mike answered "Because I'm a boy"

"Good man" Mark gave him kiss on the head and flew him around the kitchen. He put him back on the ground and then picked Matt up for his turn.

Olivia got the fudge from fridge and put it on all of the kid's ice cream "Go wash your hands guys"

"Go" Mark gave Matt a kiss on the head and put him on the ground as all three kids ran to the bathroom.

"How was work?" Olivia asked as she put the bottle back in the fridge.

Mark wrapped his arms around her waist "I closed a case, so very good"

"Congrats" Olivia hugged him "You smell good"

"Oh I put some cologne on that I had in my car"

"Why?"

"I wanted to get lucky tonight," He whispered with a smirk and as he kissed her neck.

Olivia rolled her eyes with a small smile "I'm really tired, I'm sorry"

"But you're so cute"

"I had a very long day at work sweetheart and I still have some files to review"

"Aww this is starting to sound like a real marriage" He mumbled into her neck.

Olivia chuckled a little "You get more sex then any man I know" She whispered.

"Why is that?"

"Cause I love you and you turn me on easily and you are a gentleman"

"That's what I like to hear" He gave her a kiss and let go of her "Put some Lucky Charms on the ice cream" He took out cereal and put it on all of the kid's ice creams.

"Mark don't teach them that stuff, then they will make their junk food even more junk food"

"Let them eat what they want, well not all the time but once in a while let them go crazy"

The twins and Lilly came back into the kitchen.

"You guys washed your hands?" Olivia asked looking at them. All three nodded and held up their hands. "Good. Here you go" She handed them their ice cream. "Eat it slowly"

They nodded and went to the living room.

"Want to watch a movie?" Mark asked looking over at Olivia.

"I have some things to do for work but why don't you watch a movie with them while I finish ok?"

"Sure. Don't be long though ok?" He gave her a kiss.

"I wont" She returned the kiss and went into their bedroom. She took the file under her pillow and lay down. Olivia opened the file and started to read over it.

Brad got home and placed the files he had in his arms on the kitchen table. "Guys?" He went to Ben's room and leaned on the doorway seeing Casey reading to Ben.

"Why do bunnies hop?" Ben looked up at her.

"They are too lazy to walk sweetie," Casey answered with a smile as she played with his light red hair.

"Can we go to Mike and Matt's house tomorrow?"

"Sure"

Brad smirked since Ben was always shy except with the twins, which they found weird since both Brad and Casey were very outgoing. "Any more room on that bed?"

Casey and Ben looked over and spotted Brad there.

"Hi daddy" Ben waved with a huge smile.

Brad walked over and gave him a kiss on the head "Hi buddy" He gave Casey a kiss "Hi sweetie"

"Ben want daddy to finish reading or do you want to sleep?"

"Sleep" Ben answered.

"Ok" Casey pulled the blanket over him and placed the book on his nightstand "Comfy?"

"Yea"

"Goodnight honey" Casey gave him a kiss and got off the bed.

Brad gave him a kiss on the head "Goodnight buddy"

"Goodnight" Ben mumbled sleepily.

Brad and Casey left his room and left Ben's door open just a little. Casey went to the bathroom to take off her make-up and Brad went to their room to get ready for bed.

After a while Casey came back in the room and Brad was lying in bed under the covers reading a magazine.

"How was work?" Casey asked as she took off her sweater.

"Good" Brad answered as he kept reading over the magazine. "We closed a case"

"That's good." She took off her jeans and pulled on her pajamas. "Can I ask you something?"

"Sure"

"When are we going to make it official?"

"What are you talking about?" He looked up at her totally confused.

"Marriage. We have been engaged now for two years and we haven't talked about it or planned anything"

"We've been busy at work. Almost every night consists of one of us coming home late a at night, spend time with Ben and then sleep"

Casey just nodded and got into bed and turned to the side "Goodnight"

Brad rolled his eyes and placed his magazine down "Oh c'mon now your mad at me?"

"Nope. I'm busy sleeping" Casey answered.

"Don't be like that, c'mon" He moved her hair behind her ear.

"If you don't want to get married then you should tell me not to keep my hopes up"

Brad looked down and scratched the back of his head "Look I'm scared of marriage"

Casey turned around to look at him "What are you talking about? You were the one that proposed"

"I know. I wanted to do the right thing and marry you since you were having my child but I didn't realize what I was getting into"

"Oh so now I'm an obligation to you?"

"No, no, I didn't mean it like that Casey. Just the idea of spending the rest of your life with one person scares me"

Casey nodded a little "So if you get tired of me you dump me and you don't have to worry about divorce papers huh?"

"You're making this sound more cruel then it is"

"Right. Sorry. I just found out that my fiancé…excuse me, boyfriend, doesn't want to marry me cause he is scared to have a wife and be committed to one person for the rest of his pathetic life. Tell me something boyfriend, what are you going to tell our son and explain to him why his mommy and daddy are not married? What about when he asks if he was a mistake? Are you going to keep it from him for years and then tell him the truth that he was never supposed to happen?"

Brad just looked at her "Don't treat me like one of your perps that you grill in the courtroom"

"No I'm just curious Brad, I really want to know what you would tell him once he figures out that we are not married."

Brad shook his head and picked up his magazine "I'm not fighting with you over this"

"Fine. How manly sweetie, the second you're caught and scared you don't want to deal with it" Casey shook her head and turned to the other side.

"What do you want me to do? Yell?"

"If that's what it takes for you to talk to me"

"So you would have rather I just dumped you when I found out you were pregnant? Is that what would have made you happier? I'm still with you, I care about our son, and I've never once touched you inappropriately or did something for you to think I don't care about you or our son. I thought I did the right thing by being there for you when I knew you needed me and now you have the guts to criticize me? Thank you, I appreciate it" He threw his magazine down on his nightstand and turned off the light.

"So you proposed because you thought that's what I wanted and needed so I would know you cared about him and me? It wasn't because you wanted to marry me was it?" Casey whispered still keeping her back turned to him.

"Don't tell me that you were so sure about marrying me; we dated for four months when we found out you were pregnant. We hardly knew each other Casey," He whispered still not turning to look at her.

"You're right, I wasn't sure about marrying you then but I am now…but you're not ready to marry me ever so it doesn't make a difference" She got her pillow and a blanket and got up from the bed.

"Casey c'mon"

"You didn't have to be with me if you didn't want to; I told you that you could have been involved as much as you wanted. I didn't need you to propose to me and keep making me wonder why we still weren't married after the longest time."

"I'm sorry but I thought I could get over my fear knowing a child was involved"

Casey just shook her head trying to keep her tears to herself "If you don't want to be with me then don't hurt Ben by just walking out of his life, we don't have to be together but I do expect you to be there for him since you wanted to be involved in this all the way"

"I still want to be with you"

Casey said nothing. She took off her engagement ring and placed it on her nightstand "Whom are you kidding?" She went out of the room and lay down on the couch.

Brad took her engagement ring and held it in his hand not realizing what he just did. He pushed away the mother of his child and the women he loved.

Mark was sitting on the ground with Lilly in his lap as him and the twins played monopoly.

"Pay up little one" Mark demanded.

"No, that's my house" Mike told him with a mean look.

"What are you talking about? That's Lilly's and mine's isn't that right Matt?"

"No. Its Mike's" Matt told him.

"It's ouw's!" Lilly yelled at him.

"See. I told you" Mark playfully grabbed the play money from Mike's pile.

"Daddy! That's cheating!" Mike yelled at him.

"You can't prove anything," Mark teased with a smile.

"Mom!" Matt and Mike yelled at the same time.

"Big twouble mistew" Lilly looked up at Mark.

"You're on my side, don't tell" Mark whispered to her as he gave her a kiss on the head.

Olivia came out of the room and went to the living room. "What's wrong?"

"Daddy is cheating again" Mike told her and pointed to Mark who was playfully looking innocent.

"I don't know what you're talking about" Mark shrugged.

Olivia smirked and sat down on the floor by Mike "What did he do this time?"

"Stole money"

Olivia playfully gave Mark a shocked look "You didn't"

"It was Lilly" Mark whispered and pointed to Lilly who was sitting in his lap and playing with his badge.

She looked up hearing her name and quickly shook her head.

Olivia smiled and took Lilly in her arms "No more stealing, daddy"

"Ok" Mark pouted, "I guess you two win"

"Mommy why is your badge different from daddy's?" Mike questioned looking at Mark's badge as Lilly played with it "His is smaller"

"Cause we work for different places" Olivia answered.

"Which badge does Ben's dad have?" Matt questioned.

"Like daddy's" Mark answered as he gathered all the things from monopoly and placed them in the box.

Lilly smiled and pulled herself up to be by Olivia's ear "I like Ben" She whispered softly into her ear.

Olivia smiled "I think he is coming over tomorrow" She whispered back into her ear. A huge smile appeared on Lilly's face.

"What are you two talking about over there?" Mark questioned suspiciously.

"Girl talk" Olivia answered.

"Well ok then, the men are going to sleep" Mark got up from the floor "Let's go men" The twins got up from the floor and followed Mark as he led them to their room.

"You want daddy or mommy to read to you?" Olivia asked as she got up from the floor with Lilly in her arms.

"Daddy, he does funny voices" The two year old answered with giggles.

"Fair enough" Olivia gave her a kiss on the head. Mark came out of the room and went to the two "She wants you read"

"Well ok" Mark picked Lilly up and placed her on his shoulder "Hey where did Lilly go?"

"I'm wight hewe daddy!" Lilly yelled. Olivia chuckled since Mark loved to play with her.

"What was that?" Mark teased and started to turn in circles playfully "Lilly?"

"Daddy I'm still wight hewe!"

Mark pulled her up from his shoulder and held her in his arms "Hey there you are. Where did you go missy?"

The two-year old burst out laughing and looked at Olivia "Oh boy"

Olivia laughed and gave her a kiss "Goodnight honey. I love you"

"Love you too" Lilly waved as she returned the kiss on the cheek.

"Why did you disappear like that? I was worried sick kiddo," Mark teased as he carried her up the stairs to James's room since he moved out a year ago and got his own place.

Olivia smiled watching them since all of the kids loved Mark so much because he was always goofy with them. She hated that she had to tell Mark about his real father since he was such a good father and husband that she was afraid he wasn't going to be able to handle the truth.

Olivia went back to her room and got her mother's file from Mark's drawer and lay down in bed and started to look at the notes he made. She noticed some of the people's comments that he interviewed and she always found it weird how he took notes but it made him a good agent so she couldn't blame him. Most of the notes were written on the folder or on a paper with arrows connecting the witnesses in a certain way.

She knew that most of the ideas and main points of cases were in his head since he was extremely smart and good at his job even though he never liked to show it. She looked at some parts that just had a letter or two which was his way of putting it as a reminder because he kept most of the information in his head.

Mark came in the room and closed the door behind him "I put all the kids to bed, aren't you proud?"

Olivia looked up at him and smiled a little and then back at the folder.

Mark took off his tie and started to unbutton his shirt "Aren't you done with work?"

"Just something else left to be done." Olivia answered as she got up and sat down at her computer.

Mark took off his shirt and nodded "Then are you coming to bed?"

"Yea" Olivia answered with a nod as she grabbed the Anderson file and opened it.

Mark took off his pants and threw them to the side. He walked over to Olivia and gently massaged her shoulders.

Olivia quickly closed the file feeling him there and not wanting him to know what she was doing. She looked up at him and smiled "I'll be there in a minute sweetie"

Mark gave her a weird look "Are you ok?"

"Fine. I just don't feel comfortable doing research on what I'm about to do research on with you there" She sort of lied since she knew he gave her privacy when it was something about work that she felt uncomfortable talking to him about.

"Oh" he nodded "Like something female like?"

"Yea" Olivia nodded "Just give me like ten minutes honey"

"Of course" He gave her a kiss and went to bed.

Olivia looked at him for a second and then back at the file. She read that his mother had green eyes so one of the people that he interviewed or the people on her case must be his father with blue eyes.

She finally found a name that both files had in common. Ryan Vaughn. She smirked a little knowing that had to be him. Olivia logged into the NYPD system and searched the name. After a while she finally found out that Ryan was a professor at Philadelphia. She looked at the picture and it did look a lot like Mark only older. She wrote down the address and then got up from the computer.

"Done?" Mark questioned.

She nodded and got ready for bed. She lay down by Mark and felt his strong arms embrace her around her waist. He lightly gave her a kiss on her cheek. Olivia placed her hands over his and enjoyed his scent even if she couldn't sleep with the knowledge that weighed on her for not telling her husband the information she knew.

The next morning Olivia sat at her desk twirling her pen in her fingers and just staring at the address that she wrote down. She wanted to talk to this man before anybody else, especially Mark.

She finally got up and went to her Captain's office. "Hey Cap can we talk?" She asked as she closed the door behind her.

"Sure, what's up?" Cragen looked up at her.

"This Ryan Vaughn guy who's DNA was found by our victim he lives in Philadelphia and I was wondering if I can go and talk to him"

"Well that would be smart, get Stabler and go ahead"

"Um…actually I was wondering if I can do this alone"

"Why?"

Olivia sat down across from him and played with her fingers nervously "Long story"

"Yea right" He challenged with a smirk "C'mon you can tell me"

"Warner found out that his DNA matches Mark's meaning it's his father and I haven't told Mark this yet because I want to talk to Vaughn before anybody else."

"I thought Mark's parents were dead, murder-suicide"

"So did we but we figured his mother probably had an affair which might be the reason his fath…Marcus Anderson killed his mother and then himself"

Cragen just looked at her for a second "Olivia you haven't told your husband yet?"

"I know captain but he always blames himself and he-"

"Go ahead" Cragen put his hand up so she didn't have to talk anymore since he knew how sensitive Mark was when it concerned his parent's death.

"Thanks" Olivia got up with a nod and left his office.

A couple of hours later she walked up to the house in Philadelphia with the address in her hand. She took a deep breath and knocked on the door.

A man answered the door and just looked at her "Can I help you?"

A shiver ran down Olivia's back looking at the exact same baby blue eyes her husband had "Detective Olivia Benson, NYPD. Can I come in?"