I recently learned that my grandfather was an illegitimate child.

the guy we've always assumed was my great grandfather died a year before my grandfather was born. So there's no way he's my actual great grandfather. Therefore, my last name doesn't really mean anything. I've always been kinda proud to have a very rare Irish last name, but I have no blood relation to that family. It turns out, after my great grandfather's death, my great grandmother had an affair with the neighbor whose last name was Clark. So I went from believing I had a super rare, weirdly spelled last name to finding I'm technically a Clark (one of the most boring last names in the world).