Vanessa Kirby flaunts a fake pregnancy bump in Fantastic Four: First Steps, which she says was heavier than her actual pregnancy belly. The actor is now pregnant in real life, expecting her first baby with her partner, Paul Rabil.

In conversation with Seth Meyers, who joked, "Oh, my God, it’s so cool that you stayed in character,” Vanessa, who plays Sue Storm, says, "I honestly think a lot of people think it’s a stunt of some kind. It’s just crazy timing."

On how her fake belly was created, she detailed, "Essentially, the fake belly is like a foam thing. When it’s a foam, it feels very light and a bit silly. So I kept saying to Flick, who looks after my costume, ‘I want more. It needs to be heavier.'"

However, Vanessa's request only left her with a backache. “So we would try all these different things, and eventually she kind of put heavy rice packets in the belly, and it got so heavy, [and] I got a really bad backache,” she disclosed.

"The fake bump in the movie was nothing like this. This is … way lighter. So, I gave myself a backache for no reason at all," the actor, who is a number of months into her pregnancy, said.

Also starring Pedro Pascal, Ebon Moss-Bachrach, Joseph Quinn, Ralph Ineson, and Julia Garner, Fantastic Four: First Steps marks the first film in phase six of the Marvel Cinematic Universe. The film, helmed by Matt Shakman, hit theatres on Friday and opened to largely positive reviews. Protecting Earth from Galactus and Silver Surfer presents Mister Fantastic, Invisible Woman, Human Torch, and the Thing with their most difficult task to date in the film.