Help! My Niece Has No Idea That the Man She is About to Marry is My Son

Dear Prudence,

Over 20 years ago I had an affair with a married woman who became pregnant with my child. She reconciled with her husband and they raised the boy as their own. I have not had any contact with my biological son, at the husband’s request. No one in my family knows I have a secret son. Two weeks ago I found out my niece (my sister’s daughter) is engaged, and the groom to be is none other than my biological son! Prudie, I am livid that my son’s mother and her husband did not stop this relationship in its early stages. “No, Bobby, you can’t date that girl because she’s your biological cousin” is all it would have taken. I contacted the woman and she swore she didn’t know our son was marrying my niece since my niece has a different last name. I asked her what she planned to do to stop the wedding and she said she’s doing nothing! Our son doesn’t know anything and according to her, cousin marriage is harmless! Prudie, how do I bring this up with my niece and her parents? I have never had any contact with my son and I don’t think I should approach him about it. He doesn’t know his father is not his biological father. I don’t want my niece to live in incest because of my past mistake, Please help.

—Possible Cousin Marriage

https://slate.com/advice/2025/03/niece-son-secret-wedding-cousin-marriage-advice.html