Adopted Into His Birth Family
So turns out one of my cousins was actually a different aunt child but she couldn’t/wouldn’t raise him so another aunt adopted him to keep him in the family. Only my mother and her siblings knew this until his biological mom was dying of cancer and they decided to reveal it. It was really crappy.
Especially because he has a biological sister that was little more than a long distant cousin. He was around 24 when this all came out.