I'm sure I'll get this story wrong because it was told to me over a decade ago - it was about the dad of my best friend, and it went something like this....
So my friend's dad, he was brought up in Lancashire in the 1940's/1950's by his parents, and so the decades pass, and he marries and moves up to Scotland, and his parents pass away. And he has a son (my friend) and more years pass, and he reaches his 50's in age, and then his sister dies, and he goes back down to Lancashire for the funeral.
And at the funeral are cousins/relatives of him. And at some point before or after the funeral, a relative comes up to him and they talk, and during the conversation, this person suddenly says something to him like, "Oh, well, it was hard for you what with your mum and dad not being your real parents."
It turned out that his real mother was his mother's sister, and who he always knew as his mother was actually his aunt.
And even more, the person he always knew as his dad was in reality just his aunt's husband, and completely unrelated biologically to him.
And even more, the sister whose funeral he was attending was actually his cousin.
NO-ONE had EVER told him. And the relative who told him had assumed that he knew.
The story went that back in the 1940's his real mother had a one-night stand, a fling with a guy, and she found herself pregnant and unmarried at a young age, and so she left town and secretly gave birth to him miles away over in Wales, and then she returned home, and the baby was given to her elder sister's family and brought up as their own, and he was given his aunt's husband's surname.
The sad thing is that by the time he found out, they were all gone - his mother, his aunt, his father, his sister - they were all dead. And he still has no idea who his real father is, and will never know.
ALL of them had gone their entire lives, and died, without EVER telling him.