The actress debuted her baby bump at Monday’s CinemaCon in Las Vegas, where she was promoting her new movie, "Teenage Mutant Ninja Turtles: Out of the Shadows," with co-star Will Arnett.
Fox already has two children, sons Noah and Bodhi, with her estranged husband, Brian Austin Green. Fox filed for divorce from Green in August 2015 after five years of marriage.
She spoke with People about what it was like to film the latest "TMNT" movie while pregnant.
"I’m always in the process of having a baby and looking like I didn’t have a baby," Fox said. "I was training. There was no access to healthy food on the set so I ended up losing weight because I was hungry all the time.”
Megan Fox later commented on her pregnancy by posting a picture on Tuesday of her former and current co-stars, Shia LaBeouf, Will Arnett and Jake Johnson. The actresses kept things short and to the point, captioning the photo, "#notthefather."