Robert Downey Jr. relied on caffeine to keep him going while portraying Iron Man.
The 47-year-old actor got "tired" on the set of 'Avengers Assemble' as he reprised his role as the superhero for the third time, so used the stimulant as pick-me-up.
Speaking at the European Premiere of 'Avengers Assemble' at Westfield London's Vue Cinema last night (19.04.12), he told BANG Showbiz: "Sometimes I get tired but the role never does.
"I find caffeine helps me to play Iron Man, it keeps me going. I don't have too much, just enough."
As well as being fatigued, Robert admits he was like a "nervous parent" while shooting the film because he was worried about whether it would be a success or not.
He added: "The film has turned out really well. I'm like a nervous parent when it comes to the film but fortunately for everyone it turned out great."
Robert was joined at the premiere by fellow cast members Scarlett Johansson (Black Widow), Chris Hemsworth (Thor), Tom Hiddleston (Loki) and Mark Ruffalo, who admitted shooting the movie alongside such a star-studded cast made it feel like he was in an NFL all-star team.
Mark said: "I would love to do a stand alone film as The Hulk, but that depends on Marvel and the appetite of the fans. But being in this film was a great experience, it felt like I was playing on the all-star team of the NFL."