AITAH if I tell my ex that the man he thinks is his father may not actually be his father?

I (44F) have a 16 year old son with my ex, who I’ll call J. My son has epilepsy, ADHD, bipolar disorder, and was also diagnosed with Tuberous Sclerosis (TS). When we got the diagnosis, doctors told us it appeared to be paternal/genetic, which completely shocked us.

J and I are no longer together, but during some family drama, I ended up speaking with J’s oldest sister. That conversation turned into a complete bombshell.

She told me that the man J believes is his father IS NOT actually his biological father. According to her, their mother used to be a prostitute years ago before she “changed her life.” I already knew about her past, but she later became very religious and acted like that part of her life never existed.

Apparently, the man J calls his father was a John who took pity on her because she had several children with absent fathers, and he stepped in to help raise him. Not to mention in his older sister’s words, their mother saw that man as a way to get money from him because he liked her. She didn’t like him because he wasn’t attractive enough for her, but his money was. Therefore, he became J’s father. J always spoke very highly of this man, despite having a complicated relationship with him growing up.

Before J’s mother passed away, we told her about the genetic test results showing this condition was inherited from the paternal side. Her response was:

“I don’t know where he would’ve gotten that from because none of my kids are sick.”

That statement alone raised a lot of questions for me.

Then J’s sister dropped an even bigger bomb: she claims J’s real biological father is actually their mother’s FIRST cousin.

Yes. Her cousin.

At first I thought she was just trying to hurt her mother’s image because she openly hated her, but then I looked up the cousin on Facebook… and this man looks EXACTLY like J. Even older family members apparently believe he’s the real father. Plus, J has even told me that he knows for a fact that his mother slept with another cousin of hers, he blurted this out when he was mad at her

According to the sister, their mother had a very traumatic and chaotic life and made a lot of questionable choices.

TBH I’m mad as hell because I’m thinking is my child related to an incestous family. Is that why my son has so many problems? My side of the family has things like high blood pressure, heart issues, some family members have passed away from cancer, but nothing of this nature. 

Now I want to be clear that I am not saying that those diagnosis above that my son has is because of incest, but let’s be real that people with too close of a genetic makeup can pass things to their children.

Here’s my dilemma: J keeps saying he wishes he could ask his parents questions about the genetic condition, but both his mother and the man he believes is his father are dead. However, the cousin who may actually be his biological father is still alive.

So now I’m stuck.

Would I be the AH if I told J what his sister told me? On one hand, this information could matter medically/genetically because of our son’s condition. On the other hand, this could completely destroy the image J has of his family and his mother BUT because of all their crappy family secrets I now have a sick child from that!

Do I say nothing… or tell him everything?