UzumakiDKate
"Excuse me?" Tony questioned, dumbfounded, as he stared at his mother, wondering if he had heard wrong.
"I'm pregnant tony." Maria repeated softly. "You're going to be a big brother."
She smiled at him as she spoke and tony thought his mind might explode. Pregnant?! A big brother?! This was insane, he was not ready to be a brother! Surely this was some kind of prank. He tried to dismiss the fact that pranks were very much not his parents' type of thing.
or
I started watching Iron Man: Armored Adventures and it led to this. What if instead of the typical father-son relationship, Tony and Peter were siblings? They have an 18-year age gap and tony is still in college when peter is born.