Jennifer Aniston has accidentally flashed her nipples Monday, Sept. 8, at the Toronto International Film Festival when she stepped on to the red carpet for the premiere of her upcoming indie drama film "Cake."

The 45-year-old "Friends" star, who was accompanied by her fiancé Justin Theroux and her co-star Sam Worthington, looked stunning in a black sleeveless dress with a pleated bottom at the annual event. But the Golden Globe-winner was not wearing any bra, so when cameras began to flash, her outfit turned a bit more transparent, revealing her nipples, E! News reported.

"Cake," which is directed by Daniel Barnz from a script penned by Patrick Tobin, follows the story of Claire (Aniston), a woman suffering from  addiction, rage issues, suicidal depression and chronic pain after a tragic accident that leaves her broken inside and out. Claire eventually develops a relationship with Roy (Worthington), husband of Nina (Anna Kendrick), who killed herself.

"She basically has to decide whether she wants to live or die," Aniston, who is also serving as an executive producer on the film, told Variety about her "beyond dream role." "The woman's journey is so heartbreaking but so uplifting, because she's gone through a trauma but maintains her wit, which is very endearing."

Aniston revealed that she knew she was going to do the film the moment she had finished reading the script. Though she acknowledged that taking on the role was a challenge, Aniston saw it as an opportunity "to express empathy" for the character and all those individuals facing similar experiences.

In order to make her portrayal more believable, Aniston allowed herself to be photographed with greasy hair and no makeup.

"It's awesome and liberating to let that all go," the actress told People about her makeunder for the role. "And see yourself looking like that on a 50-foot screen."

Every movement for the character is painful, "which was hard on my body for five weeks of shooting. I spent weekends seeing a chiropractor and getting massages and trying to maintain my sanity," she told Variety.

"Cake," which is still looking for a U.S. distributor, received favorable feedback from critics most especially for Aniston's performance. In fact, the actress got a standing ovation from the audience after the film's premiere, according to People.