Zac Efron has been picking more mature roles since graduating from High School Musical and in new film, The Lucky One (which opens on Wednesday, May 2), he shows off a whole new side, as he strips for his first sex scene. The blue-eyed boy talks about the responsibilities of playing a US marine, his intense training for the role and of course, those love scenes.

By Shereen Low.

It's almost impossible to resist Zac Efron's boyish charms.

Even if you're not a fan of High School Musical, the Disney Channel series that turned him from unknown teenager into hunky heart-throb, it's easy to see why scores of teenage girls have waited outside a London hotel for hours, just to catch a glimpse of him.

Even with the fingers on his left hand bandaged up in gauze, which he jokingly blames on an over-zealous fan, Efron oozes sexiness in a custom-made black suit and fitted white shirt. And with his slicked back brown hair, one lingering gaze with those piercing blue eyes is enough to reduce most grown women - and some men - into giddy teenagers again.

His post-High School Musical moves have been eagerly anticipated, as people watched earnestly to see how the 24-year-old would shake off his Disney role. And while each film - from The Life And Death Of Charlie St Cloud, Me And Orson Welles and New Year's Eve (in which he locked lips with Michelle Pfeiffer) - has taken him further away from those teenage outings, his latest movie, The Lucky One, could arguably be his most mature yet.

In Scott Hicks's big-screen adaptation of the Nicholas Sparks novel, Efron plays US Marine Sergeant Logan Thibault, who returns home after serving his third tour of duty in Iraq.

"Initially, I wasn't convinced I could pull this off, but the more I thought about it, and the more I talked to Scott, I realised if there was ever going to be a chance to play a role so different from what I've played before, this was it," says Efron, as he orders a "green tea with ice".

"I knew that it would be a challenge, but that's where the fun comes in."

Playing a soldier suffering from post-traumatic stress disorder (PTSD) is new to the actor, who has never strayed too far away from his comfort zone. To make sure he was doing the part justice, he took the opportunity to speak to real-life Marines at Camp Pendleton in California.

"It was like stepping into a different world. They were very normal guys other than their posture and the way they present themselves: they stood with a purpose, they had laser focus and never broke eye contact," he recalls.

"They had immense dignity. Never once did they let on how traumatising it was until they started telling their stories, and even then it wasn't weepy, you could just see it in their eyes that they had been there and experienced some pretty gruesome things."

Next came the physical transformation: gone is the floppy, boyish hair, replaced by a buzz cut.

"I have never had it that short. I didn't know if my head had bumps on it," he admits, with a sheepish grin.

"It was pretty symbolic cutting it all off. Boy, was that weird! But it was a really great feeling," he says.

If the haircut helped him step further away from his Disney persona, his recent antics in public have also asserted his new-found independence. At the LA premiere for The Lorax in February, he accidentally dropped a condom on the red carpet, while in an interview on Jimmy Kimmel Live, to promote The Lucky One, he beat the host at a bra unhooking competition. He's certainly grown up and has the physique - and a tattoo on his right hand of YOLO (You Only Live Once) - to match.

Efron had to undergo gruelling training with retired Sergeant Major James Dever for four months to pass for a seasoned Marine.

"It was the most intense training I had ever done," he says.

Fans will also see a whole new side to Efron in the film, as he strips off for his first steamy love scene.

How does he feel about the hysteria that happens every time he shows a bit of skin?

"I don't really know how to put it into words. It's better than the opposite reaction," he admits, focusing on straightening the tablecloth.

"I try not to think about it at any point. That's one thing I don't notice; I'm looking at all the flaws. I'm looking at the performance more until my mum says very loudly: 'That's my boy!' Then you go: 'Oh, my God'."

He gives due credit to leading lady Taylor Schilling, saying: "Heck, I had a great partner - we kind of got lost in it.

"I thought she was beautiful when I first met her. She's unafraid of trying anything, she's very good to work with."

As for the sex scenes, being surrounded by a nervous crew and having a relaxed director helps dispel any awkwardness.

"Everyone is tense on those days, it's not just us. It's kind of like a built-in awkwardness," says Efron, lowering his eyes.

"Taylor and I knew each other very well by this point. I tried to make her as comfortable as I could, which was just to laugh it off."

While Efron, who previously dated his High School Musical co-star Vanessa Hudgens, admits to being more "easy-going and gregarious" than "serious" Logan, it's clear that he's taking time to make the right career moves and has set up his own production company, Ninjas Runnin' Wild, under Warner Bros.

"I want to make cool movies that I would watch. Anything that's innovative, that's new," he explains.

Efron will next be seen in Josh Radnor's indie drama Liberal Arts, which premiered at Sundance London, and he's off to Cannes for Lee Daniels's The Paperboy - which sees him working those love scenes opposite Nicole Kidman.

"Lee Daniels took a risk on me for that part. Every time I had a scene with Nicole, I felt like I was in Moulin Rouge - I was so in love with her," he says.

Efron, who counts his family as his lucky charm, believes destiny has played a part in his life.

"I know that I was in the right place at the right time and there are moments when I just think: 'It's too good to be true'," he says.

"Maybe fate presented me with opportunities, but it's the hard work that gets you the right film."

He wants his career to be an education and is not taking anything for granted.

"I didn't start picking roles because I'm the best actor on the block - I sort of came in and now I'm making an effort to learn as I go, so if I'm not stretching or really growing with every role, I don't know how much longer I can be around."

Extra time - From page to screen The following Nicholas Sparks books have all been adapted for the big screen: :: A Walk To Remember (2002, Mandy Moore and Shane West) - Boy meets girl. They fall in love. She falls ill and dies.

:: The Notebook (2004, Ryan Gosling and Rachel McAdams) - Boy meets girl. They fall in love. Girl breaks up with boy. They reunite, then die.

:: The Last Song (2010, Miley Cyrus and Liam Hemsworth) - Rebellious girl meets boy. They fall in love. They break up, then reunite.

:: Dear John (2010, Channing Tatum and Amanda Seyfried) - Boy meets girl. They fall in love. He goes off to war. She gets married to another man, who later dies. They reunite.

:: The Lucky One is released in cinemas on Wednesday, May 2