Posting on behalf of SIL!
SIL has a 16 year old DS. The man he thinks is his father isn't in fact his father.
She had an affair, got pregnant at 15 but the man didn't want to know and went back to his pregnant wife!
So DNephew has a half sister he doesn't know about and the person he thinks is his dad actually isn't.
The real father got in touch when DN was 6 months old and said he wanted to be involved but SIL told him she wasn't interested and that DN would never know anything about him.
However, MIL is now pushing for SIL to tell DN about his real dad and has threatened to contact the real dad (via FB where she's found him)
I know it's none of my business and I wont get involved or give my own opinion but SIL has asked me to post on here. Does anyone have experience of this?