It seems that the Marvel Multiverse brings out the ultimate creative side of its fans. When Tony Stark and Steve Rogers became enemies in Captain America: Civil War, loads of theories (beyond the obvious) emerged to explain the bad blood.
For some people, blood had everything to do with it. Some theorized that Peggy Carter, love of Captain America’s life, was the mother of Tony Stark (aka Iron Man). Supposedly, the flirtatious way that Howard Stark (Tony’s father) speaks to Peggy during The First Avenger movie could have led to them getting together after Captain America crashes into the ice and is presumed dead.
However, the timelines don’t work with this theory. In addition, writers for the Marvel Cinematic Universe (MCU) movies have confirmed that the intent was always for Peggy’s two children to have been fathered by Captain America.