Jennifer Garner accidentally flashed her Spanx shapewear at the Hollywood premiere of Alexander and the Terrible, Horrible, No Good, Very Bad Day on Monday, Oct. 6. Credit: Splash News Online

Spanx a lot! Jennifer Garner accidentally flashed her nude, tummy-tucking undergarment at the Hollywood premiere of Alexander and the Terrible, Horrible, No Good, Very Bad Day on Monday, Oct. 6.

Garner, 42, looked resplendent in a black LBD by Valentino, featuring a multilayered, tiered skirt. The star was laughing with her castmate Steve Carell when she pulled her clutch to the side of her body, exposing the slimming shapewear.

Without letting her wardrobe malfunction deter her from enjoying the night, Garner went on to conduct several interviews before heading in to the screening. In the movie, Ben Affleck's wife and Carell play a married couple, who constantly scold their troubled son Alexander (played by Ed Oxenbould). The film is based off the beloved 1972 children's book by Judith Viorst of the same title.

One of the film's stars, Sidney Fullmer, who plays Becky Gibson, told Us Weekly what it was like to work alongside the Alias actress. "She was so amazing to work with," Fullmer gushed to Us. "She has such a loving and nurturing nature about her. It was so great to be around her on set."

The mother of three attended the premiere solo, as her husband is currently busy promoting his new drama Gone Girl. The couple, though, were together this past weekend when they were photographed exchanging kisses outside of a farmers' market in L.A. See more pics of the couple's PDA.