Is Robert Downey Jr. Really Returning As Tony Stark/Iron Man And Not Doom In "Avengers: Doomsday"?

What is your biggest film fan theory? I have an insane fan theory about the upcoming 'Avengers: Doomsday,' and that is that Robert Downey Jr. isn't actually playing Doom but a Tony Stark/Iron Man variant? I have no evidence online to back this up, but that's the best part of watching movies is to be a fan. It is possible that he is playing both Doom and a variant, which would make more sense. It's…