Robert Downey Jr. thinks the 'Iron Man 3' script is the "best" he has read.

The 46-year-old actor is set to reprise the role of businessman Tony Stark/Iron Man for the fourth time - following on from the character's appearance in ensemble comic book movie 'The Avengers' - in the highly anticipated film, and he admits he is excited to get working on the Shane Black-directed feature.

Speaking at the UK premiere of new movie 'Sherlock Holmes: A Game of Shadows' at the Empire Leicester Square, Robert told BANG Showbiz: "'Iron Man 3'? It's the best script I've read in five years. It's going to be a phenomenal theatre-going experience."

Filming on the movie is set to begin early next year ahead of a summer 2013 release.

Just a few months ago Robert - who was joined by stars Noomi Rapace and Jude Law at the premiere - admitted he did not know the story to the film.

He said:"We're not talking much about The Script right now because Shane is off writing and we talked before that and when we are talking again the talking is going to be over pretty quick because we're on the same page.

"It's kind of like we're fighting on the same side and at the same time we're circling each other so it's all great. It should be great."