A family member has been looking into her family history on her dad’s side. He left when she was 8, and never came back apart from one time to see her mum.
He’s dead now, but it’s transpired that he remarried and had another child.
As far as we’re aware, this child (who is now an adult) doesn’t know that she has 6 other siblings. Family member isn’t interesting in contacting them, but one of her siblings has said that she thinks she ought to know, and she is going to get in touch with her, possibly even turn up on her doorstep. 
I have suggested this might be a bad idea, especially doing it in such a crass manner, but she’s adamant that she has the right to know this sibling, and they ought to know that they had a family they didn’t know about. She’s a bit peculiar is this woman, and is one of those who has to believe that she’s always right about everything 
I don’t think there’s anything we can do to stop her, so the question is, would you want to know?
IMO this could turn her whole world upside down. Not only would she find out that she wasn’t an only child, but she would then also find out that her father had a whole previous family she knew nothing about.