So I've never met my bio dad. Him and my mom divorced when I was too young to remember and I was raised by my step dad. I've never really questioned anything about him, I know his name and that he's dead now and that's about it.

So I've always been somewhat curious about my father's side, but never really looked into it, but ancestry had a sale so I decided to take their DNA test. Well I was matched with someone who the website says is my father. I messaged him once and when I told him my mom's name, he never replied again.

Awhile later a female that came up as a close relative asked who I was, I told her and explained my story. Turns out her dad is also the guy that I was matched as my dad and she is in the DNA range of being my half sister. I tried to get more information from her, but she doesn't want to tell me who he is and no longer will talk to me either.

So obviously according to my DNA, the man I knew as my bio dad isn't. Should I bring it up to my mom or let it be? I'm 26 so it's not going to make a difference now, but still that's half of me that I know nothing about. How would i even bring that up to her?

TL:DR- took an ancestry DNA test, found out the man that is supposed to be my dad isn't. Should I tell my mom?

UPDATE: I still haven't talked to my mom, but the girl who I was talking to before (his daughter) ended up confronting her dad and asking about me. It turns out he had been a sperm donor and I'm guessing that's what happened. I forgot to say that I knew I was from IVF, but they never told me that used a donor. This also makes sense because I have 3 other matches that fall in the range of being half siblings also, guess he was a popular donor. I'll probably just let it be.