Zac Efron, 24, doesn't have to do much to convince people he's growing up. Efron went from being in a High School Musical to training as a Marine for his new role in Scott Hicks' The Lucky One, based on the eponymous novel by Nicholas Sparks.

"His desire to play the part [of ex-U.S. Marine Sgt. Logan Thibault] was palpable," Hicks, who also directed Shine and Snow Falling on Cedars, told USA Today. "My question to Zac was, really: 'How are we going to do this? Obviously, on the face of it, you're not built like a Marine."

Efron noted that the transformation from slight-to-bulk for The Lucky One wouldn't be easy, but it didn't cause him to shy away from the role written by The Notebook writer Sparks, which Efron called "a damn near perfect movie." Playing Logan Thibault was something Efron was determined to do. "The character wasn't exactly like anyone that I'd played before. Marines have a different sort of persona than I think I carry personally and … I thought there's a chance I could pull it off with the right amount of hard work, and it would be worth it to transform."

And transform he did, training between two and four hours every day with retired Marine Sgt. Major James Dever, who has worked to bulk up such actors as Nicholas Cage, Tom Cruise and Aaaron Eckhart. "He's just like young Marines that I always worked with," Dever said of Efron. "That's what I loved. He liked to kind around just like the young Marines do, but he also takes it seriously, too."

For anyone who still doubts that Efron is no longer that High School Musical kid, it takes only a glimpse into last month's news, when Efron dropped a wrapped condom from his pocket on the red carpet premiere for Dr. Seuss' The Lorax, on which he voiced the character Ted. "I never really had a pocket-checking policy prior to going on the red carpet before, but now we've fully instated one," he told the Today Show after the condom-dropping incident.

In the same vein, his next role in the erotic thriller, The Paperboy, involves a steamy love scene with actress Nicole Kidman. "I felt like I was stepping into Moulin Rouge," Efron said of the scene. "I'm a big fan of Nicole's for a long time," he added. "That one my heart was racing for."

But right now everyone's heart is racing for Efron, plus the 25 lbs. of solid muscle he packed on for The Lucky One. During the hardcore training, "It was me and a fellow actor and like 50 Marines, real Marines. So I would just say to the guys, 'Tell me if there's anything I'm doing that doesn't look legit. Get my back here. And they were so great. That was probably one of the most fun days that we had. Just thinking back to High School Musical, I never though I'd be doing that."

Well, we're glad you did. You can feel like the lucky one watching Efron's new toned physique on April 20 in theaters.

Watch Efron's Today Show interview here:

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