Derek averts his wide eyes to his mother and then to his sisters, all reflecting the same expression as his head feels like it's going to explode. Little James' words give him a clue, but it's the women's expressions that confirm the story that is unfolding in front of him, Addison has his child.

Quickly Caleb, Liz's husband gets up and starts to gather his children and nephews with the excuse of watching a movie in the bedroom. Fortunately John, Dylan and Amy follow suit and soon the four manage to drag 14 disgruntled young Shepherds upstairs.

Alone with his mother and three of his sisters, Derek lets out a deep breath before asking,

"Do I even have a son?!"

It sounds like a stupid question but it's Derek's way of organizing his thoughts and when the women nod he asks:

"Where is he?"

"In New York with Addison."

Nancy explains in a soft voice and Derek asks:

"How long have you guys known?"

"Since Addison found out."

Nancy confesses with her eyes downcast, at which point Derek jumps off the couch yelling:

"That's almost two years!"

"Darling, calm down."

Carolyn asks softly, but the son retorts:

"I can't calm down, Mom!"

"I always said you should know, but I was outvoted."

Says Liz. Nancy frowns and replies to her sister:

"Please Elizabeth, don't act like we did this out of spite, because you know we didn't."

"It wasn't mean, it was childish!"

"Enough, you two! And Lizzie, you know damn well we couldn't betray Addie's trust, not when she came to us so fragile."

Carolyn ends the daughters' argument as she's done her whole life and then turns to Derek to placate:

Derek, you have every right to be angry, but you need to calm down so we can talk about it like adults."

Derek nods still annoyed and sits down again demanding:

"I want to see my son!"

"Sure, I'll call Addison and tomorrow..."

"I want to see my son today, now!"

Derek sternly interrupts, but Nancy isn't intimidated:

"Derek you know it won't work, we can't go to New York at this hour."

"What if you warn her and she runs off with my son?!"

"Don't be ridiculous, Addison would never do that."

"She's run away before!"

"She didn't run away, she came back to New York before she knew she was pregnant."

Nancy claims and Derek tries to argue again:

"And when he found out he wasn't able to casually call me and let me know. The result is that I missed the first few years of my baby's life."

"Now Derek get off your high horse. This all just happened because you hurt Addison, you gave marriage a second chance just to be the good guy and made her life miserable."

Nancy talks totally impatiently and leaves Derek speechless. Since he was a teenager he hasn't received such treatment from one of his sisters and that surprises him, especially since he can't say anything, after all Nancy is right.

After a few seconds of silence, Derek asks in a much calmer tone:

"Do you have pictures of my son?"

Carolyn smiles and gets up quickly, she opens a dresser drawer in the living room and takes out two picture frames handing them to Derek. As she does so, irritation surges through Derek again, after all clearly the photos were kept from him, but as soon as the portraits are in his hands, he forgets about the matter.

In the first photo the boy is smiling brightly, while wearing a tuxedo in a clearly posed photo. In the second he's also smiling in na outfit with teddy bear ears, the tiny teeth just starting to show. Derek's eyes fill with tears at the realization that his son is not only the most beautiful child he's ever seen, but he's also the perfect blend of him and Addison. As James had said, the boy has red hair, but the strands are clearly thick and curly like his father's, as are his impossibly blue eyes and he could have sworn he was seeing the Shepherds' noses.

After some time admiring the photos he looks at his mother proudly stating:

"He's beautiful!"

"Yes he is."

"Chris is the most beautiful baby in the world!"

Says Amelia entering the room. Derek's eyes turn to his sister as he asks,

"Chris?"

"He has daddy's name."

Amelia confirms with a soft smile and Derek asks:

"Why?"

"Because we were all there for Addie, especially Mom and I, it was her way of saying thank you."

Amelia speaks with a slight accusing tone that Derek doesn't miss. Before further discussion begins, Carolyn intervenes:

"I have a whole album I can show you later, honey. Now what else do you want to know?"

"What's his age?

"One year and six months."

"But..."

"He was born premature."

Carolyn explains anticipating her son's confusion and Derek asks in alarm:

"Why, what happened?!"

"Addie had a risky pregnancy."

Carolyn explains again, not wanting to go into detail that Addison is the one to tell. Derek says to himself:

"And she was alone."

"She wasn't alone, I postponed my residency and moved in with her. And Archer was there every day, besides Mom Nancy... She was just without you."

Amelia says dismissively and Derek simply gets up off the couch and walks briskly out of the house. Carolyn and Lizzie give Amelia dirty looks and then Kathleen suggests:

"Give him time to digest all this."

"I'm going to call Addison."

Nancy says taking her cell phone and getting up from the couch. The other women are still in the same place, also assimilating the latest events.

The phone only rings twice before Addison's cheery voice picks it up:

"Hey Nance, Merry Christmas!"

"Thanks, Addie."

The ex-sister-in-law's tone of voice does not go unnoticed and Addison asks in a cracking voice:

"What happened?!"

"Addison, I'm sorry!"

"NO! Who told?!"

"James and Lily, I asked for secrecy, but they're just kids. I'm sorry."

Nancy asks quite upset and Addison dismisses:

"It's okay, they're kids. It's just not supposed to go out like this..."

"I know..."

"How did he react?"

"In the Derek Shepherd way you know."

Nancy states in a monotone and hears Addison sigh on the other end of the line. After a few seconds of silence, she explains:

"We'll be there tomorrow, probably before lunchtime."

"Okay. Thanks for letting me know."

Addison affirms and ends the call without saying goodbye. Nancy returns to the room.

Derek remains outside for a long time alone, until the door opens and his mother approaches, stopping beside the old wooden bench, saying:

"It's freezing out here, honey."

"I always wanted to be like daddy."

Derek speaks out of nowhere and Carolyn lets out a heavy sigh before sitting on the bench next to her son. She puts her hand on his thigh and continues:

"I wanted to be a husband like he was and I failed. I know Addie cheated on me but I wronged her first, I treated her the way Daddy would never treat you."

"Derek..."

"And now I've failed as a father. My son is almost two years old and I didn't even know he existed."

"This isn't your fault, Derek."

"I told her I loved Meredith, I told her that on Christmas Eve."

Silence descends after that, it's the first time Derek has talked about that night in two years and it's awkward. He's always seen what he said to his ex as sincerity, but when he thinks about it coldly, it's more like cruelty. After a few moments he spoke again:

"I knew she wasn't okay. She was acting Montgomery mode, distant and passive aggressive, I knew she wasn't okay and I didn't apologize."

"You had no way of knowing."

"But if I had apologized, if I had fought a little harder for my marriage, she wouldn't have left. If she hadn't left, we would have found out about the pregnancy and everything would be fine."

"Really?"

Carolyn's tone of voice makes Derek turn towards her for the first time since the beginning of the conversation, she caresses her son's thigh as she explains:

"A child can't be the only thing holding a couple together, Derek. You and Addison weren't working long before Seattle."

"But she still loved me."

"Is that you?"

Carolyn asks arching her eyebrows and Derek looks away, before he can answer, Liz's nine-year-old son Luke arrives complaining:

"Grandma, Uncle Derek, you need to go to sleep too so Santa can show up."

Carolyn gives her son na amused look and Derek ends up smiling before nodding. So the two get up and follow the boy into the house, the conversation totally unfinished.

Derek lies alone in his old bedroom, almost nothing has changed in the room since he moved to Maine at eighteen. It's a familiar place, the place he shared with Nancy for awhile as a child, the place where he and Mark played so many video game matches, where he hid for days after his father's grisly death. It's the place where he's sneaked in with some girls, trying to avoid questioning from his curious mother and sisters, and the place where he's slept with Addison more times than he can count. Thanksgiving, Christmas, New Year's Eve and Easter nights where she was overjoyed to be with family, where they planned that next year they'd add a baby, even though their careers would always make them put off those plans.

So Derek wonders if his child has ever been in that room, if the baby has ever slept in his bed. It reminds him of the photo that used to be on the bedside table, obviously it's not there anymore, but after developing Christopher's photos it's easy to deduce and when he opens the drawer, he smiles.

It's a photo of the day after medical school graduation, he's sitting at his mother's kitchen table, smiling while Addison has her arms around his shoulders, mirroring the same smile as his amazing eyes twinkle at the camera.

The photo was taken by Amy who at the time was obsessed with photography, the next day her mother developed it and put it in a picture frame, giving them a copy, he wonders if Addison still has it.

Derek then places the exposed photo on the table and lies down again, fantasizing about what his first date with his son will be like.

Derek wakes up on Christmas morning as anxious as his little nephews, he goes straight to the kitchen where mother and sisters are gathered and demands:

"Come on, Nancy!"

Nancy lets out a deep sigh and starts gathering things, deciding not to upset her brother.

As the obstetrician leaves the kitchen, Carolyn approaches her son, she adjusts her jacket collar as she asks:

"Take it easy today. Don't let your son's first date be a bad day. And listen to what Addie has to say."

Derek just nods and kisses his mother's forehead, at which point Nancy returns to the kitchen with the car keys in her hand. Derek then escorts his sister out of the house and into the car.

Once they're on the road Derek starts the conversation trying to find out more about what happened to Addison:

"Did you take care of her during her pregnancy?"

"Me too."

"How many months was Chris born?"

"Seven. He spent almost a month in the NICU."

"It must have been a nightmare for Addie."

Nancy doesn't answer and Derek stares at her asking a little alarmed:

"Nancy what happened anyway?"

"A lot of things have happened, Derek, but these are things Addie should tell you. Things that will help you understand her better."

Derek nods and is silent for a few moments before asking,

"But they're fine now aren't they?"

"They look great. I've never seen Addie so happy as when she's with Chris."

Derek smiles at that, thinking how natural Addison has always been with kids, and how sure he's always been that she's going to be a wonderful mother.

After a few more seconds of silence he asks:

"Does she have anyone?"

"Why are you jealous?"

"Of course not. I just want to know if there's a man around my son!"

Derek speaks irritably and Nancy lets out a small laugh before explaining:

"She's had a boyfriend for a few months. He's also a doctor and is friends with Samuel and Naomi in Los Angeles."

Derek grimaces upon hearing this, Nancy rolls her eyes, deciding to tease him some more:

"But his father figure is really Archer."

Derek frowns and Nancy doesn't even have to look at him to feel his indignation explaining:

"He was there throughout the pregnancy and he's still very much present, he's the best man. He and Amy, by the way."

"Archer Montgomery and Amelia Shepherd are my son's godparents? The people who would stay with him if something happened to his mother?"

"First this is morbid, second they are amazing godparents. Very present."

"While I don't even know my son. I get it, Nancy."

Derek barks angrily and once again the older sister rolls her eyes before explaining:

"That's not what I meant."

"You know what? It doesn't matter and I want to be silent now."

He speaks in the same tone as before and leans against the window. Nancy lets out a heavy sigh and then turns her attention back to the road. The rest of the trip passes in complete silence.

As the car starts to turn into familiar paths, Derek snaps out of his sulking position and looks back at his sister as he asks,

"Does she still live in Brownstone?"

"Why the surprise? That house is amazing."

Derek nods, the house is amazing and awash with the second worst memory he has in his life, his wife in bed with his best friend. Obviously for Addison this shouldn't be a bother, she's never shown genuine regret, at least that's what he thinks.

When the car finally pulls up in front of the Bronwstone, Derek feels his stomach sink as memories wash over him. His last night in that house, seeing Addison and Mark together, throwing the clothes and Addison herself out of the house, stepping out into the rain determined never to see his wife again. That night changed his life and who he was forever. Noticing her brother's hesitation, Nancy squeezes his hand and speaks softly:

"You can do it."

Derek nods, he clears his throat, lets go of Nancy's hand, and gets out of the car, walking briskly up the stairs.

When they stop at the door, it's Nancy who rings the doorbell.

It doesn't take long for the door to open and the air leaves Derek's lungs as he comes face to face with his ex-wife for the first time in so long. They stare at each other in awkward silence, looking into each other's eyes, while Derek's expression is stunned, Addison remains utterly stoic.

This chapter took a while as I've been really busy.

Thank you for your comments, they always encourage me a lot.

Addison is coming to season 18 again!