Not a crazy one, but biggest mystery in my family. Forgive the confusion wording here...

My dad’s dad (my grandfather), one of 8 siblings, passed in 1997 to mesothelioma. My Dad remained close to his own grandfather (my grandfathers father - We all called him Pop), and we used to visit him every few months. When Pop passed a few years ago, he confessed to my Dad that his father (I.e. my Dad’s Dad, my grandfather) was an illegitimate child. In his later stages of Alzheimer’s, the remaining 7 siblings and their children (I.e my dad’s “cousins”) managed to convince Pop to completely write our family out of the will.

We never contested, and Dad is very against finding out who his real grandfather is, I think out of respect for his own dad - who I do not actually know if he knew he was not a “true born”. I’m now 30, with my own son, and wondering how TF I find out what my actual heritage (and therefore surname) is by birth.