I have one from ages ago. I never see any of the people involved and haven't for years.
Elderly ex-MIL has elderly couple friends going back decades. I know the friends, as we have stayed with them. They are a married couple who got together six decades ago, at university.
MIL told me that when the couple were 18 and dating, the wife - then the girlfriend - got pregnant and gave the baby up for adoption. I suppose it must have been during their first year of university. The couple then stayed together, got married, and had three more children. They remained together for about sixty years, until the wife died of old age a couple of years ago.
I found it very sad indeed, that they stayed together for the rest of their married life and had lots more children, but that the first child they made together was adopted. I have no idea if the adult children - now in their fiftes/early sixties - have any idea whether they have a full sister out there, and I dearly wished my MIL had never told me their secret. We would go to stay with the elderly couple, and I was terrified that something would slip out.
MIL showed me the profile of the first baby from Facebook. She's about seventy now, and, heartbreakingly, is the spitting image of her birth mother. I've met the couple's adult children, from back when we used to stay with the elderly couple, and I have NO IDEA if they know about this secret sibling. If not, it seems so wrong that I know and they don't. Anyway, I haven't seen them in years, and I won't, because their mother died, and the connection was the friendship between her and my MIL. Who's my ex-MIL, anyway. I don't even know if the husband is still alive. If so, he must be ninety.
It's so odd that they didn't have any contact with the child, but I suppose adoptions were closed back then and they never talked about such things. But I have wondered how the couple felt over those years, knowing that their kids had a full sibling out there. The whole thing sounds desperately sad, and I so wish my MIL had never said anything to me.
Also, the first baby was a girl, and the three subsequent children were all boys. Makes it sadder somehow.