Mum and Dad divorced when I was a kid, he moved 80 miles away and my siblings hadn't spoken to him for 40years when he died, I always did with exception of a few years when we had a fall out that later resolved itself when his 2nd wife told me what had been going on, or so I thought.
In his 80's, I nursed him through a terminal illness, his 2nd wife was too frail and had dementia. He was in and out of consciousness towards the end and doped up on morphine.
He started a conversation about his life regrets, the way he treated my mum, his multiple affairs (he left mum for wife 2) and included having split up with his 2nd wife for a while (all news to me) in the 80's. At that point he had a relationship and there was a child he had met a couple of times, he said his 2nd wife knew nothing about it as he drifted back into unconsciousness. I was shocked and my instinct was to shout him awake to tell me the rest but I didn't as I thought we had time. He lived for another few weeks but was out of it, he didn't know who I was and we never got to finish the discussion.
I wasn't aware he and his 2nd wife had actually split, I knew they had some problems and I'm assuming it was mid 80's when we had fallen out, it all fits with what happened at the time.
So I have a half sibling somewhere, no idea male or female, name or when born (other than poss mid 80's) or who to. Couldn't say ask stepmum who he was with as she was in lala land and as older people do they had drifted away from their friends or they had already died. The only person who may have known was his older sister and she had advanced dementia and has since died. Never told my brother and sister, didn't want them to be struggling with the idea like I do.
I am on DNA website and hope someday someone will pop up.Its good to be able to write it publicly, only my husband and best mate know. I'd like a younger sibling!