Kristen Stewart was spotted wearing one of Robert Pattinson's T-shirt in L.A. (Photo : REUTERS/Mike Cassese )

Kristen Stewart takes on her sexiest role in her latest film, "On the Road." In the film, which is an adaption of Jack Kerouac's famed book, Stewart will appear topless.

The once squeaky clean actress has been shedding her innocence this past summer. Stewart was caught having an affair with her married "Snow White and the Huntsman" director, Rupert Sanders. Though she's suffering from backlash for ruining a marriage and cheating on her "Twilight" co-star Robert Pattinson, the actress has gained a rebellious edge.  

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Stewart says she wasn't nervous about her first on-screen nudity "It didn't bother me," said told MTV news at the Toronto Film Festival. She credited her comfort to her director Walter Salles. It seems like  the actress has a great appreciation for her director. "You can do no wrong with [Salles]. He puts so much inside of you," Stewart gushed.

"In the four-week rehearsal process, it was okay to ask any question, to bring up any story, to really overanalyze everything and intellectualize everything."

Stewart did not think getting half-naked would be too serious. "Once we got on set, it was so about just breathing and letting it happen. He put so much trust in us," she continued. "So it was like, 'OK, so I have to take my clothes off?' It's so not a big [deal]."

Maybe before when she was a teen, the actress would feel uncomfortable doing nude scenes. But now, the 22-year-old "Breaking Dawn actress feels secure and comfortable in her own skin.  "I should have definitely been older than 17 while playing this part, absolutely," she said. "[My performance] would have been done very differently if I was younger. I wouldn't have played the part, obviously."

Stewart excitedly took on the role of Marylou because of a desire to explore the fearlessness of the world Kerouac wrote about in his novel."I don't want this to be misconstrued in anyway, but you do want to get as close to an experience as you can," said Stewart. "Anything that feels guarded, in this particular movie especially, would just be so against the spirit of it."

 "On The Road" will hit theaters on December 21.