Brad Pitt Mingles with Girlfriend Ines de Ramon at 'Babylon' Premiere Afterparty

Brad Pitt and Ines de Ramon were seen together at the Babylon afterparty in Los Angeles on Thursday

Brad Pitt had his girlfriend Ines de Ramon by his side Thursday night, at the Los Angeles premiere of his new movie Babylon.

The Oscar-winning actor, 58, was seen with the jewelry executive, 32, at the afterparty for the new film — the two mingling with guests, occasionally with their arms around each other.

Their outing comes a month after PEOPLE confirmed the pair "have been dating for a few months." They were first photographed together on Nov. 13, alongside Cindy Crawford and Rande Gerber, backstage at a Bono concert at Los Angeles' Orpheum Theatre.

Brad Pitt. Emma McIntyre/WireImage

According to the source, "Brad is really into" de Ramon, who separated from her husband, Vampire Diaries star Paul Wesley, earlier this year. "They met through a mutual friend. She is very nice," the insider added.

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"Ines is cute, fun and energetic. She has a great personality," a second insider said, noting the two aren't yet exclusive. "Brad enjoys spending time with her."

Brad Pitt; Ines de Ramon. Kurt Krieger/Corbis via Getty; Alberto E. Rodriguez/Getty

Babylon follows Pitt as fictional movie star Jack Conrad in 1920s Hollywood, amid a transition from silent to sound films.

The film is written and directed by Oscar-winner Damien Chazelle.

Speaking to PEOPLE Thursday on the red carpet at the Academy Museum of Motion Pictures, Pitt opened up about the "intense" filming schedule of the decadent 1920's comedy-drama, which also stars Tobey Maguire, Olivia Wilde, Jean Smart, Jeff Garlin, and Pitt's Once Upon a Time... in Hollywood costar Margot Robbie.

"We have 700 extras, doing a war scene in the background. We're trying to catch it right when the sun goes down," Pitt said. "That's really what movie-making feels like. You're losing the light, everyone's racing, jamming, to try to get this thing just right and we've only got this window of time and that's it. It's locked into cement. It's intense."

"So there's a moment of that in the film that's really beautiful," he added.

Brad Pitt and Diego Calva in Babylon. Scott Garfield/Paramount Pictures

Pitt also revealed to PEOPLE why he believes costar Diego Calva is destined to become Hollywood's next been thing.

"He's just solid. He's just solid. He knows what he's doing," he said of the 30-year-old. "You know he walked into this film and he's really the lead, and then there are multiple characters that all cross paths in the silent movie era, but really all revolves around him — it's through his eyes, he carries it."

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Margot Robbie and her mother Sarie Kessler on the Babylon red carpet. Emma McIntyre/WireImage

As for Robbie, she shares a kiss with Pitt in the film — a moment she improvised.

"I thought, 'When else am I gonna get the chance to kiss Brad Pitt? I'm just gonna go for it,' " she told E! News earlier this month, noting that the scene "was just great" as she detailed how the talk with Chazelle went.

"I said, 'Damien, I think Nellie would just go up and kiss Jack. And Damien was like, 'Well, she could — wait, hold on. You just wanna kiss Brad Pitt,' " Robbie, 32, recalled. "And I was like, 'Oh, so sue me. This opportunity might never come up again.' And he was like, 'It does work for the character,' and I was like, 'I think so.' "

After one take, Chazelle, 37, was persuaded, according to Robbie. "He was like, 'No, do it again. That really works.' I was like, 'Oh, great,' " said Robbie.

Babylon hits theaters Dec. 23.