EXCLUSIVE: Anne Hathaway Says She Lied While Pregnant to Protect Her Child

The actress insists that she's usually a "very, very bad liar."

Anne Hathaway insists she's usually a "very, very bad liar" -- except when it came to her pregnancy.

"I get very flushed when I lie, so I am very bad at keeping secrets. People can always tell what's up," the 33-year-old actress tells ET's Cameron Mathison at the Toronto International Film Festival while promoting Colossal. "The only secret that I kept, and I will tell you I got really good at lying, was when I was pregnant."

She adds, "I lied about everything having to do with it."

WATCH: Anne Hathaway Posts Body-Positive Message to Moms -- ‘There’s No Shame in Gaining Weight During Pregnancy’

Hathaway explains that she chose to be untruthful about her pregnancy as a way of shielding her child-to-be. "I did not feel like, 'Oh, I am lying,'" she confides. "It was like, 'No, I am protecting.'"

She quips, "I am a boxing-out mama bear."

WATCH: Anne Hathaway Reveals the Horrible Post-Baby Gym Encounter That Made Her Cry

Hathaway and husband Adam Shulman welcomed their baby boy, Jonathan Rosebanks, in March. A few months later, she spoke to ET about shedding her pregnancy weight and how Shulman was doing with fatherhood. Check it out:

Colossal, in which Hathaway plays an alcoholic writer who discovers she has a psychic connection with a monster destroying Seoul, South Korea, is slated to hit theaters in 2017.