Robert Downey Jr is annoyed Chris Evans hasn't called him in six months.

The 49-year-old actor, who stars as Tony Stark/Iron Man in the Marvel movies, has revealed he's ''crazy'' about Evans - who plays Captain America - but is annoyed that he hasn't been in touch in so long.

Asked what made him want to appear in 'Captain America: Civil War', Downey Jr joked: ''I'm crazy about Evans. I really am. I don't know why or how to explain this particular kinship we have. By the way, he hasn't called me in six months.

''Honestly, in order for this whole thing to have worked, I did my part, [Chris] Hemsworth knocked it out of the stadium and then it fell on Cap. That was the riskiest. It was the one that had the highest degree of difficulty in making it translate to a modern audience.''

Downey Jr also previewed the role of Tony Stark in the new movie, suggesting his character will take on a darker tone.

Asked whether he'll appear as the bad guy in the film, he told Empire magazine: ''I wouldn't put it that way. Ultimately it's [Captain America/Steve Rogers's] story; it doesn't say 'Iron Man 4: Civil War'. I think that's great too.

''I think Chris [Evans] has been hungry to bring even more of an underside and some shadow to that. I remember the comics - on the surface you got the sense that Cap was baseball and apple pie, but underneath there was all this churning stuff of being a man out of time.

''Now we know he's made his peace with that. What's the bigger issue? It can have a little something to do with the past, but it can be about someone becoming more modernised in their own conflict.''