Robert Downey Jr. says Avengers Assemble is the "one instance" in his life when everything has gone well.

The actor reprises his role as Tony Stark/ Iron Man for the new film, which boasts an all-star cast including Scarlett Johansson, Samuel L. Jackson, Chris Hemsworth, Tom Hiddleston and Chris Evans.

Captain America, Thor, Black Widow and The Hulk all appear in the movie and Robert knows some fans were concerned about how so many big characters would work together. He insists there is no need for scepticism.

"You know, I'm not one of those people who wants to be [all], I just don't understand why everything's gone this well!' But that, in this one instance in my life, seems to be the situation," he told Cover Media.

Robert first played the character for 2008's Iron Man and hasn't looked back since. He knew there was a lot on the line with Avengers Assemble due to the star-studded cast and admits to being fearful of the effect it could have on some of his fellow actors.

"From five years ago, when we did the first Iron Man, to today with all these folks you see up here it honestly couldn't have gone any better," he said. "All three franchises that we've launched so far had to work. If this didn't work than it affected all of the previous franchises extremely adversely and there's also the potential for additional franchises based on how strongly people are reacting to Jeremy [Hawkeye] and Scarlett [Black Widow] and Mark [The Hulk]."

Avengers Assemble sees the group of superheroes joining forces to protect the earth.

It hits cinemas in the UK on April 26.