I know that I am going to kick myself when someone answers this, but I really don't remember where I read it. Steve and Bucky come back from the war, and go see Howard where they meet a young Tony. Howard doesn't pay much attention to Tony because he is an omega. It turns out that once Tony is a teenager, Steve and Bucky are his mates.
Trigger warning Non-con:
Howard attempts to molest Tony during his first heat (Tony was early), since Howard had not found an alpha to be with Tony during his heat.
Thank you lots!