Ashlee the Star at 'Undiscovered' Premiere

LOS ANGELES – She has a supporting role in the film, but Ashlee Simpson (search) was the star attraction at the world premiere of "Undiscovered."

A drama set against the backdrop of the Los Angeles music scene, the film, which comes out this weekend, follows two young lovers struggling to strike a balance between career and romance.

Simpson marks her major feature-film acting debut as the couple's best friend Clea, a classically kooky but wise sidekick.

"I definitely didn't want to take a lead role," Simpson told APTN as she entered the Tuesday night event. "And it was definitely a conscious effort, because I wanted to work with actors that were really good, and that could help me with my acting. And choosing the role of Clea was really a lot of fun because I could just be grimy and dirty and not wear makeup, and live in an environment where it's not about beauty, it's just about learning."

By many accounts, Simpson, 20, was a quick study.

Noted co-star Pell James (search), "I didn't know what to expect because I'd seen her on TV and heard her music, and this and that. And, then, working with her, she's a total pro. Like I would forget my lines, and she would know them. It was embarrassing."

Premiere attendees included all of the film's principals, as well as Simpson's on-again, off-again boyfriend, pop idol Ryan Cabrera (search).

Conspicuously absent was Simpson's singer-actor sister, Jessica Simpson (search), who, Ashlee explained, simply couldn't make it to Los Angeles in time following Monday night's London premiere of her own film, "The Dukes of Hazzard."

Ashlee said she prepared for the premiere by getting a seaweed wrap at the Burke Williams Spa. After going with jet-black hair and manly attire for the film, she was back to blonde and glamorous in a classic black Marc Jacobs dress and white pumps.

The event inspired Simpson to recall her own discovery.

"I think getting the opportunity to be on the show '7th Heaven' was my first kind of big gig that I got to do," she said. "And signing my record deal, that was a moment of going, 'Wow! I'm actually going to make my own record.'"

Of course with fame comes more attention — not all of it good. Witness Simpson's October 2004 "Saturday Night Live" (search) incident during which a national television audience discovered she was lip-syncing to a pre-recorded vocal.

Simpson addresses the matter on her new CD, "I Am Me," which is set for an Oct. 18 North American release. Just before the record's release, she'll sit down with Oprah Winfrey, to give her take on the "S.N.L." incident.

Simpson's father and an "Undiscovered" producer, Joe Simpson, confirmed reports that Ashlee was in negotiations for a return to "Saturday Night Live."

Ashlee reflected, "I definitely experienced so much this year: every high and every low, and I think it's been the most amazing year I could have possibly had, because I have learned so much."