This makes no sense to me

I have been ruined by Renekton in a few games recently, at least in early game, so I decided to research him and find out the best ways to play against him. (Pretty much if you're not ranged, you're screwed early game, and even then......) But while I was researching I came across some of his lore. Now I may be WAY behind the times and I may be bringing something up that has been brought up over and over and over and over and over and over... I think you get the point. (I am not sure why but I just had a Spongebob memory of the Frankendoodle episode.....)

Anyway, I discovered that Renekton and Nasus are brothers. What the heck? I understand that this is a game and a lot of things are possible but really?

? + ? = +

To make my brain stop hurting, I am going to assume one of them was adopted.