Henry Cavill plays Superman in the upcoming blockbuster "Man Of Steel," but in a new interview, the actor reveals that he didn't always have the ripped body of a superhero.

As a child in boarding school, "I was fat. I was Fat Cavill," he tells Details in its July issue, adding that he was also prone to homesickness. "I bawled on the phone to my mom four times a day. I became an easy target."

To combat the loneliness, Cavill began acting in school plays and ultimately decided to study drama. At 17, he landed a role in a film adaptation of "The Count of Monte Cristo," and "lost one and a half stone [21 pounds]," he says. "I wasn't Fat Cavill anymore."

Now, Cavill, who is 30 and dating former mixed martial artist Gina Carano, is a bit shy about revealing his weight ("It's modesty. . . but I also don't want to invite that debate: 'Henry weighs this, so he's the perfect Superman.' Or, 'Henry doesn't weigh this, and therefore he's not believable in the role,'" he explains). But it's no secret that the Tabata workouts that his trainer Mark Twight used to prep him to play the Man of Steel were tough.

"Henry's commitment was legendary," says co-star Amy Adams. "He would get up to work out at three every morning so he'd look right in the suit. His discipline is extraordinary."

"I was a lot bigger as Superman," acknowledges Cavill, who began principal photography on the film two years ago. " [But] I'm not eating 5,000 calories a day anymore!"