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OTRC: Zac Efron on bulking up for 'The Lucky One': I was intimidated

Zac Efron appears at the premiere of 'The Lucky One' on April 16, 2012 in Los Angeles.

Zac Efron gets into a more adult role in "The Lucky One" where he plays a Marine returning from Iraq but the transition wasn't easy for Efron, whose lean build didn't fit his character.

So in order to play the role, Efron underwent training with Logan Hood, a former Navy SEAL who worked with Efron to bulk up the former teen heartthrob. The 24-year-old actor started out at 145 pounds and gained 18 and a half pounds for the role, according to an interview he did with Men's Health for their May issue. Efron also visited with Marines at Marine Corps Base Camp Pendleton in San Diego County, California.

"I was intimidated," Efron told OnTheRedCarpet.com at the premiere of "The Lucky One" on April 16 about gaining the weight. "I remember the first day I went to Camp Pendleton and I said, 'I can only imagine what these guys must be thinking. Who is this guy?'"

"We brought it to Camp Pendleton and they really liked the film," he added.

Efron also said he didn't think he could handle the role at first. "It just seemed like a challenge in so many ways. It was a role that I didn't think I was necessarily suited for," he said. "I knew it would be a great challenge."

"I knew I had a great director - Scott Hicks - attached to it, who is somebody I would be blessed to work with at any point in my career and he was someone who could guide me through this experience," he added. "Also it's Nicholas Sparks. I think that he writes great characters. He really, really has an amazing, amazing eye for what's going to make a good film."

"The Lucky One," which hit theaters on April 20, is based off the Nicholas Sparks novel of the same name. The actor plays a Marine named Logan Thibault who survived three tours of duty in Iraq. Logan credits his safety to a photograph of a woman he found while in Iraq and sets out to find out who she is. He later discovers the woman is named Beth (played by Taylor Schilling) and he begins working at her dog kennel to try to work up the courage to reveal his story.

When asked about filming love scenes with Schilling, Efron said, "We had a great time. We knew each other really well at that point so, I always have a sense of humor with it."

The actor made headlines in February when he dropped a condom on the red carpet at the premiere of "The Lorax." He later joked about the incident saying, "I never had a pocket-checking policy prior to going onto the red carpet before, but now we fully instated one prior to going on the red carpet."

Check out the trailer for "The Lucky One" below.