It didn't take long for Megan Fox to get her pre-baby body back.

Just 53 days after she and Brian Austin Green** welcomed a son, Noah, the actress attended a private screening of her new movie, This Is 40, in Beverly Hills Nov. 19. Wearing skinny jeans, a black tee, a navy blazer and platform pumps, the new mom looked radiant as she walked into the Writers Guild Theater.

Fox, 26, broke the news of her son's arrival via Facebook Oct. 17, several weeks after she gave birth. "He is healthy, happy and perfect," the Jennifer's Body star gushed. "I am forever grateful to God for allowing me to know this kind of boundless, immaculate love."

While promoting his TBS series Wedding Band Nov. 6, Green, 39, thanked another celebrity mom for inadvertently assisting in keeping their son's birth a secret. "We got really lucky. . . Reese Witherspoon actually gave birth, I think, the day before us in Santa Monica," the actor said on Ryan Seacres**t's KIIS-FM radio show. "We were lucky enough to go in at 2:30 in the morning to the hospital and nobody knew. We were there for two days . . . and we heard Reese was at her place and had a baby, and we got out of the hospital and nobody knew [about us.]"

He added, "We got home and thought, 'This is unbelievable.' Because we weren't expecting to get away with it. So we just figured we would go with it as long as we could."

Witherspoon -- who welcomed son Tennessee with husband Jim Toth Sept. 27 -- has an ice cream cake "on the way," Green joked.

This article originally appeared on Usmagazine.com: Megan Fox Unveils Slim Post-Baby Body 2 Months After Giving Birth