Rating: PG
Characters/Pairings: Arthur/Gwen, Merlin, Tom, Balinore, OC (Marie- Gwen's Mum)
Word count: 1389
Summary: Old love letters reveal a family secret.
*Written for Fic Battle (Mini Challenge 6) on ag_fics
prompt from mustbethursday3: Gwen & Merlin (& Arthur to some extent), Balinor and Gwen's mother had an affair (he didn't cheat on Hunith, but she cheated on Tom) - Gwen and Merlin are half siblings; Arthur may just think this is the most hilarious thing he's ever heard. *bonus points if Gwen has magic too.

Written Proof
Tom decided it was time to sell the big house and find a nice flat in a retirees building. His wife Marie had lost her battle with cancer and it was too hard to stay in the house where they raised their family, especially now when he was all alone.

While he looked for the perfect flat, he had Gwen clearing out the attic, garage and the cellar. They were stuffed full of old odds and ends that needed to be gotten rid of.

Arthur was more than happy to lend a hand if it meant scoring a few points with his father-in-law. He and Tom had been at odds lately and it was important to Gwen that they got along.

Merlin pitched in as well. He had an eye for things that had some value and it never hurt to have a bit of extra cash.

Merlin and Gwen were in the attic looking through trunks when Gwen found the letters that would change everything.

Gwen pulled the box out of the trunk and looked inside.

"What is my father's handwriting doing on letters in a trunk in your attic?" Merlin asked as he looked over her shoulder.

"I don't know but our families have always been close, Merlin." Gwen said as she closed the box and dropped on the floor.

Merlin who was much more curious picked up the box and pulled out one of the letters and started to read it. "Gwen, these are from my father to your mother." Merlin stopped reading and looked at Gwen. "These are love letters."

"I don't remember Mum ever saying she dated your Dad." Gwen wondered out loud.

"That's probably because these are dated after Elyan was born and before you and I were born." Merlin said.

"She was married. She couldn't have… she wouldn't…." Gwen said as she stared at the box.

"Gwen, I think they had an affair." Merlin said. "He talks like they had a secret."

"I think an affair is a big secret, don't you?" Gwen said.

"Wait! When is your birthday?" Merlin asked.

"I just had it remember you were there, 30 August." Gwen fished in the trunk again.

"Yeah, but what year?"

"1980 why?" Gwen looked up.

"I wasn't born until 1986. He's talking about his child in these." Merlin said.

"You must have an older sibling somewhere. It's a shame he's passed on or you could have asked him." Gwen said.

"You mind if I take these? There may be a clue as to who this child is." Merlin said.

"Sure. But you have to tell me what you find out." Gwen said as she pulled an old table cloth out of the trunk. "This is a mess." She threw towards in the rubbish heap. It hit Arthur as he was coming up the stairs to get her.

"Guinevere, we need to get going we have work tomorrow." Arthur reminded her.

"Is it that late?" Gwen looked surprised.

"Its past 10 and your father just went to bed. I don't think he would want you two banging around up here. Merlin, you have to work tomorrow too." Arthur said.

Merlin grabbed the box with the letters and started for the stairs.

Arthur put his hand on Merlin's shoulder. "Don't be late. We have a meeting with Father first thing."

"I know." Merlin nodded and headed out.

Gwen looked at the mess. "I suppose I have to come back tomorrow after work to get some more done."

"I'll help. We need to get him settled. This house seems to upset him. Where ever he looks there is a memory of your mother. It would upset me too if I lost you and had to live where we had spent years together." Arthur admitted.

"Merlin is right. You are mushy." Gwen hugged Arthur.

"Hmph!" Arthur responded. "So is he, but I hide it better."

Gwen laughed as they walked down stairs arm in arm. They headed home for the night after Gwen looked in on her Dad.

Merlin sat on the bed with letters all around him. He had read every one at least twice. There was no question but the letters said that Gwen was his half-sister.

His father, Balinore, had an affair with Gwen's mother, Marie. Marie was married to Tom but his father had yet to meet his mother. Merlin had a strange sense of relief for his mother, Hunith.

Merlin wondered if Gwen shared his 'gift'. No one but his mother knew what he could do. If Gwen had the same abilities then she was indeed his half-sister.

"I know who my secret sibling is." Merlin told Gwen over lunch the next day. "I have a half-sister."

"Really? Do you know your half-sister's name?" Gwen looked up from her salad.

"It's you." Merlin said with a smile.

"That can't be, Merlin. Mum would have told me if Dad wasn't really my biological father."

"Maybe she was ashamed of betraying your father. I wonder if he knows about it." Merlin thought for a moment. "I think you should ask him."

"I will not! I am not saying a word to him. If this is true then I don't want to hurt him. I don't even know if he had knowledge of the affair. It's bringing up things that are just hurtful for no reason." Gwen put down her fork. She had lost her appetite. This was all too disturbing.

"Then how do we proceed?" Merlin asked. "If you are my sister then I want to know for sure. Your Mum and my Dad are both gone now so who do we ask?"

"What about your Mum? Maybe your Dad told her something." Gwen countered.

"I already did. She had no clue that Dad even had another child." Merlin said.

"We could take one of those tests that compare our DNA. I wonder how we get that done." Gwen frowned. "If we are really half siblings, we do not tell my Dad or your Mum. Agreed Merlin?"

"Agreed." Merlin nodded. "I'll check into getting a test done. Are you going to tell Arthur?"

"I'm not sure." Gwen said as she picked up her bag. "I have to get back to work. Call me later?"

"Yeah." Merlin said as she rushed off. He would wait to ask about the one thing he was most curious about, magick.

By the time Gwen finished work, she was really upset. How could her Mum do that to her Dad? What if her Dad isn't really her Dad? It wasn't as if she didn't know Balinore. He and Hunith were always around when she was growing up. She and Merlin had been best friends since they were small children. It all didn't make sense. She doubted it would ever would.

Arthur could tell there was something on her mind when he came to pick her up after work. Gwen got in the car and didn't give him a kiss like she was in the habit of doing.

"What did I do?" Arthur said as he started the car.

"Huh?" Gwen looked at him confused. "I'm not upset at you. I found some letters in the attic. My Mum had an affair with Merlin's dad and now Merlin thinks that he and I may be half siblings."

"That is crazy. Marie was devoted to your father. There was no way she would have done that. What does your Dad say?" Arthur glanced over at her.

"I'm not going to say anything and you aren't either. Understand?" Gwen gave him a serious look.

"Got it." Arthur frowned. "What are you going to do?"

"Merlin wants to do a DNA test." Gwen said with a sigh.

"It will give you an answer." Arthur told her. "You should do it. I can't believe that Merlin could be your brother. It's just too ….odd."

Gwen pulled out her mobile and rang Merlin. "Merlin, let's do the test…."

One week later Gwen and Merlin open the envelope to the truth. They are half siblings.

"Gwen, can you do things with your mind?" Merlin asked.

"You mean like this?" Gwen looked at the tea pot and it lifted off the table and poured tea into her cup.

Merlin lifted the biscuit plate with his mind and made it hover in front of her. "Biscuit?"