maybe duder can fuck his mom's clone? 
You could make a brother-son 
Vaguely related. My mom told me a story way back of some neighbours she kinda knew.
There was a lady I'll call grammy and her daughter I'll refer to as mammy.
Grammy had mammy youngish and mammy was hitched having a kid youngish too.
Then grammy also had a kid later.
So mammy had a sibling that was younger than her own kid. And the grandkid was older than his/her own aunt/uncle.
Fucking whack ass shit that was lemme tell you.