Jennifer Garner Spills Spanx Secret

Jennifer Garner Spills Spanx Secret

ET Canada recently sat down with a very pregnant Jennifer Garner to talk about her new film Butter, a quirky comedy about the competitive world of butter-carving which she also produced.

The ensemble film starring Hugh Jackman, Olivia Wilde, Ashley Greene and Alicia Silverstone has been three years in the making -- about as long as it took her to sign on the all-star cast.

Garner remembers trying to convince Jackman in particular, joking, "For Hugh I had to crawl and write a long email, and say, 'Dear Mr. Jackman' ... It's a big deal to ask someone to trust you and come and work on your tiny movie for no money in the middle of Louisiana."

MORE: Watch: Jennifer Garner and Hugh Jackman Make 'Butter'

The mother of two looked stunning at Butter's Toronto International Film Festival premiere, rocking a blush pink Valentino dress and a sexy pair of Casadei heels despite the extra belly weight.

And what's the 39-year-old's secret to getting red-carpet ready while pregnant? Spanx!

"You just wear mama Spanx instead of regular Spanx, and you just try and find something that you can wear," she says.

Check out the video to see Garner work that pregnancy glow at her big premiere.

MORE: Jennifer Garner is Pregnant