The actor, who turned 59 on Sunday, celebrated his birthday with girlfriend de Ramon, 32, in Hollywood, California.
The two were seen getting out of a car, with Pitt dressed casually in a gray button-up, matching slacks and white shoes.
Meanwhile, the jewelry executive wore a tan coat with a furry white lining, her hair hanging in front of her shoulders in loose waves.
PEOPLE confirmed in November that 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.
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De Ramon accompanied Pitt at an afterparty for his new movie Babylon on Thursday. Afterward, a fashion-industry source close to de Ramon told PEOPLE that Pitt “is clearly very into her, given he brought her to his premiere.”
“Ines said that Brad is very sweet,” the insider went on, noting that the pair “are planning to spend New Year’s Eve together.”
RELATED VIDEO: Brad Pitt Spotted with Ines de Ramon at Bono Concert Outing with Cindy Crawford and Rande Gerber
Meanwhile, a source close to Pitt told PEOPLE the pair are “dating and happy,” adding, “It’s not serious yet but he’s comfortable and they’re having fun together.”
A separate insider said the Bullet Train actor “enjoys dating Ines” and they “hang out when they are not busy.”
The latter source added, “Ines is fun and social. They have a great time together. They do solo dates, but also group dates with friends.”