Robert Downey Jr. continues his cinematic hot streak as a journalist who befriends a homeless musician, played by Jamie Foxx, in 'The Soloist.' In addition to talking about the impact of the movie, he reveals a few 'Iron Man 2' secrets in the process!

"The film is almost entirely about character, and yet we still have twice as much action as we did last time, so it's going to be nuts," Robert tells our own Thea Andrews of the super sequel, set to start filming Monday. "Essentially 'Iron Man 2' is about looking behind the armor, or the armature, of a superhero. It's one thing to say you're Iron Man, it's another thing to be fully ready to do that."

Robert says he's no longer on his strict 'Sherlock Holmes' diet and has returned to some serious iron to once again portray Tony Stark: "I'm on Beefcake Charlie status," he jokes. "I've got to not be the skinny Brit anymore. I have to be the Tony that you know and may have loved."

As for co-star Scarlett Johansson, who plays the femme fatale Black Widow in the sequel, Robert says, "We've been rehearsing and she's in insane shape. She's getting lean and mean."

Based on a true story, 'The Soloist' (in theaters April 24) stars Robert as Steve Lopez, an L.A. Times journalist in search of a good story. He meets Nathaniel Anthony Ayers (Jamie), a homeless man who has a clear musical talent, despite working with only two strings on his violin.

"I knew it was going to be a tough, tough job," says Robert of Jamie's role. "You get to see if the person you're working with can [take on this real-life character] and do it with grace and dignity, and he did."

Lopez decides to write about Ayers, and soon discovers that he was once a Juilliard classical music prodigy whose promising career was sidelined by schizophrenia. Initially reluctant to take responsibility for Ayers, Lopez chooses to get involved with the troubled genius, leading to a life-changing friendship.

"I would spend hours and days with [director Joe Wright] and our crew and we had to ingratiate ourselves to [the homeless of L.A.], and I just found it to be a really, really wonderful, heartwarming thing," says Robert. "Rather than try to make them part of our cast, we became part of their community, and I think that's largely what the success of the film rests on."

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