Pregnant Vanessa Kirby Says Fake Fantastic Four: First Steps Belly Was Heavier Than Her Actual Bump, Gave Her a Bad Back Ache

Vanessa Kirby is getting real about the differences between a fake baby bump and her real one.

During her appearance on Late Night with Seth Meyers on Wednesday, July 23, the actress, 37, opened up about the differences between having an actual baby bump versus using a fake belly for her role in The Fantastic Four: First Steps. In the latest Marvel film, she stars as the superhero Sue Storm (a.k.a. Invisible Woman) who becomes pregnant by Pedro Pascal’s Reed Richards (a.k.a. Mr. Fantastic).

“Oh, my God, it’s so cool that you stayed in character,” host Seth Meyers joked, referring to growing baby bump.

“I honestly think a lot of people think it’s a stunt of some kind. It’s just crazy timing,” Kirby said before detailing what went into creating her pregnancy on-screen. “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.’ ”

“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 really bad backache,” she revealed. “And actually it’s nothing like this. This is … way lighter. So, I gave myself backache for no reason at all.”

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Kirby first confirmed she was pregnant and expecting her first baby with boyfriend Paul Rabil when she walked the red carpet in a form-fitting dress for the CCXPMX Film Festival in Mexico City in May 2025. While posing, she cradled her bump.

A few weeks later, Rabil shared the happy news on Instagram alongside a photo of him holding her stomach. “Some news…life’s greatest adventure is beginning soon,” he wrote in the caption. “We’re very grateful for your love and support. Especially the advice. Mum’s a superhero. I’m just really lucky.”

In an interview with PEOPLE, Kirby said she admires the journey her character goes on throughout The Fantastic Four: First Steps. “Sue was never sat down. She was never huffing and puffing about it,” she said of her character’s pregnancy.

“It didn’t define who she was,” the Eden actress continued. “She was absolutely a mother, and of course, in the comics, that’s so definitively her. But she’s also been a team member that defends, that goes up against great threats.”

“I literally had the lived experience of somebody who was doing this incredibly sacred thing and fulfilling what she needed to do at the same time as a woman and a team member, and that changed me,” she added.

Kirby and the retired lacrosse player went public with their relationship on Instagram in November 2023.

At the time, Rabil, 39, posted a series of photos of the pair together, as he wrote in his caption, “From the very minute we first met in Des Moines, around the world and back, life is far better, more purposeful and more beautiful with you ❤️.”

Back in April, Kirby posted a series of romantic photos on Instagram of the pair vacationing in the West Indies. “What a beautiful time away to stop for a second to appreciate the people you most love,” she wrote in her caption, sharing loved-up snapshots of herself and Rabil.

“Thank you so much @fsnevis for making us feel so welcome and for having us in such a special place. 🤍,” continued the star.