"Great! Yeah, I'm in love again," he gushed when asked about becoming a father again. He also shares a 5-year-old son named Jack with his ex, Evan Rachel Wood.
When asked if he has any pearls of wisdom for new parents, he kept it short and sweet: "Sleep when they sleep."
Sources told ET in January that the pair was expecting their first child together. They confirmed the news in February when they showed up at Elton John's Oscar party. Mara posted a photo of herself alongside Bell while showcasing her baby bump in a sparkling gown. She captioned the image, "Went on a date with our bun in the oven."
On May 27, Mara shared a touching post on Instagram revealing that their new bundle of joy had arrived.
"We had a baby a couple weeks ago… Here are her feet," she captioned a sweet image of their newborn.
At Wednesday night's premiere, Bell also chatted about the Elton John biopic, in which he plays Bernie Taupin, the singer's friend and frequent collaborator while Taron Egerton takes on the lead.
"I'm excited to see-- for people to get to see Taron's transformation that he's done," he shared. "I think he's done a phenomenal job. I think the reviews from what I've seen have been phenomenal and really kind of hailed him as a great performance, I know it's true. So yeah, I'm excited for people to just go and have fun at the movies."
The 33-year-old actor also hinted at the happy accidents which transpired during the making of the film that simply can't be planned.
'Rocketman' Trailer Shows Off Taron Egerton's Impressive Singing Skills as Elton John
"It's the things that you are unprepared for," he explained. "It's the things that kind of catch you by surprise that you kind of-- whatever that kind of chemistry that happens on set between actors and filmmakers and stuff. It's that stuff that you're always kind of-- you hope will happen and it's an accident that it does but, hopefully, you capture as many of those accidents as you can."
"I haven't seen the movie [yet], but I've heard the music and [Taron] has done the most phenomenal job with the music," the singer told ET prior to the film's premiere at the Cannes Film Festival. "Our songs are not easy to sing. They're not. They're quite complicated. 'Don't Let the Sun Go Down on Me,' 'Tiny Dancer' aren't straightforward songs to sing. He really put every fiber of his body into that, into the singing, let alone the acting. He's worked double hard."