Happily married father of three here. I just found out that my (28F) niece is my youngest (20M) son's half sister.

I'll just go straight to the point.<br><br>I have a sister who has a daughter. She had her daughter when she was 14. This was something of a family scandal which we have always been hush-hush about. We never really spoke about the father, and as far as I knew it was because the guy was a deadbeat that didn't even know he was a father. Well, it turns out that isn't entirely true.<br><br>My son has a girlfriend now, and they are thinking about taking things to the next level, and my wife and I were just talking about how we needed to discuss safer sex with him. That when a thought struck me. I am a doctor, and I was so glad that my own sons couldn't possibly be the deadbeat baby daddy of anyone. I then thought about my nephews (my brother has 3 sons). I thought to myself, "Well at least none of them are the baby daddy". I then thought about my other nephews (my wife's sister's kids, she has 2 sons). And was about to think the same thing when I paused. For some reason one of those kids stuck in my head. And then it hit me. Why he looked so much like my parents. Why he was so easily integrated into our family. And how my wife reacted when my sister's daughter was staying with us for a little while. It just didn't add up. Racially he could be family. There was no issues there. My family is from Mexico, and my wife's family is from Argentina. Which is why I didn't even consider it at first.<br><br>I dug through some of his pictures, and low and behold ended up looking at a picture of my parents holding him as a baby. It was the same as one they have of me. I have now confirmed that my wife's nephew is actually my son. Which makes him my niece's half brother.<br><br>What do I do. I am at a loss here. My wife and I have been happily married for almost 25 years. I have no idea how to handle this. I keep thinking that it is too good to be true, but everything lines up. I just don't know what to do.<br><br>&#x200B;<br><br>EDIT: Wow, I wasn't expecting this many responses. To answer a few questions I see a lot in the comments:<br><br>1. My son's age: He is 20, which puts this at being while we were engaged, but before we were married.<br><br>2. Where was I: I was in medical school, and my fiance and I were in a long distance relationship.<br><br>3. Why I didn't know: The only picture I have seen of the boy was as a baby. With no adult in the picture. When I saw him as an adult for the first time, it was at a family even where he was a kid. I had no reason to think anything of him. I didn't see him much. I was told he was my wife's nephew. I assumed he was the son of her sister.<br><br>4. I am certain: I have confirmed this through multiple pictures of him and my parents, as well as my wife basically confirming it.<br><br>5. Other: The vibe I am getting from my wife is that she wants this kept quiet. And she is right, if this were to get out it could effectively destroy our entire family. But that isn't really an option. My children are involved. This will have to come out at some point.