Credit: Charles Eshelman/FilmMagic

Spoiler alert!

Kristen Stewart shares a whole new side of herself in the indie flick Welcome to the Rileys: her backside.

The Twilight Saga star, 19, plays a 16 year-old runaway stripper and occasional prostitute in the movie, which premiered at the Sundance Film Festival in Park City, Utah on Saturday. In her first scene, she dances on a stripper pole wearing platforms, fishnets, a micro-mini skirt and a bra, and eventually offers a lapdance to costar James Gandolfini. In several later scenes, audiences catch a glimpse of Stewart's bare rear end. Her raunchy character swears like a sailor and stashes cash in her underpants.

On the red carpet Saturday, Stewart admitted to reporters that she was a bit freaked out "the first time I put on all the fishnets...I really tried to own it though." She shot the indie weeks before Twilight's blockbuster release in fall 2008. "I was able to walk around the streets," she explained. "I was literally walking down the street in cut-off shorts and a robe that was cinched. I looked like a crackhead!"

"My character's not sultry, not sexy," Stewart clarified. "She sort of throws herself into all her moves. I tore myself up doing it."

And her first time up on the stripper pole -- she trained with a stripper for two weeks -- was a little traumatic. "I wanted to do it in my clothes," she explained on the red carpet. Her stripper trainer 'was like, 'No, you don't stick to the poll when you do that.'"