I've got a half sibling who I have never met. Ddad was married before he married my dm and had one child in that marriage.
As far as I know he had no contact with them after the divorce.
Ddad died over 20 years ago and I never thought I would see this sibling or find out anything about them.
I know their birth name. Whilst using ancestry.com I got a match which showed my Ddad's first marriage. After a bit of facebook hunting I'm 99% sure I've found them, and they live a 10 minute walk away from me!
I'm sort of intrigued to meet them but I'm well aware they may want nothing to do with me, as my ddad wasn't in their life and they probably feel he abandoned them. So I'm sure they won't have any good feelings towards him.
I think they might know I exist as my aunt (now also deceased) told me once my half sibling visited her sometimes. I think she would have said something as she liked to gossip about all family members.
I can't decide if it's a good idea or not to try to make contact.