It's not dark, but my father (18 at my birth) 's father would have died in his 60's shortly after my dad was born. My mom does ancestry stuff and all my dad knew growing up was that he probably had a sister about 20 years older than him. Mom found her, and the evidence of my grandfather being married 4-5 times, with at least that many kids, with about a 15 year gap somewhere in the middle.

My aunt is like 60 now and has mentioned a sibling or two, plus many many kids and grandkids besides. It's bizarre to think that contemporary, my dad has half- siblings already dead of old age, and nieces and nephews his age. Who are my cousins, and my age-mates would actually be my 2nd-3rd cousins or so.