What a vixen! 

Kristen Stewart looked like a knockout at the AFI Fest screening of On the Road at Grauman's Chinese Theatre in Hollywood Nov. 3. With her hair pulled back into a ponytail, the 22-year-old actress revealed her toned midriff in a cleavage-baring Balenciaga ensemble. Stewart completed her look with black Christian Louboutin heels. "The outfit was a mature look for her," an onlooker tells Us Weekly. "She looked really pretty."

PHOTOS: Kristen Stewart cheats on Robert Pattinson

When Stewart and her costars Amy Adams (in Dolce & Gabbana) and Garrett Hedlund (in Prada) hit up the Audi and Stella Artois sponsored afterparty at the Roosevelt, the Twilight star changed into a more comfortable look: a sheer tee (which exposed her black bra), a leather jacket and Seven jeans.

Inside the soiree, Stewart's boyfriend, Robert Pattinson, 26, was "being social with lots of different people," an attendee tells Us. "He seemed like he was letting Kristen do her thing since it was her film and she had to schmooze with industry people and friends."

PHOTOS: Kristen Stewart and Robert Pattinson's undercover PDA

Though Stewart was caught cheating with her married Snow White and the Huntsman director Rupert Sanders in July, she and Pattinson have since reconciled. "He started thinking nobody else would understand his life," a Pattinson pal told Us in September. "His rational voice told him not to toss a three-year relationship for one infidelity."

PHOTOS: Robert Pattinson's sexiest looks ever

Earlier this week, the on-again loves began jointly promoting The Twilight Saga: Breaking Dawn - Part 2.

This article originally appeared on Usmagazine.com: Kristen Stewart Bares Toned Midriff, Shows Cleavage at On the Road Screening