Brad Pitt and Girlfriend Ines de Ramon Were 'Very Cute and Flirty' at His Birthday Party: Source

Brad Pitt enjoyed his weekend birthday celebration with girlfriend Ines de Ramon and friends.

The Oscar winner turned 59 Sunday, marking the milestone the night before at the Los Angeles restaurant Pace, a source tells PEOPLE.

"Brad had a birthday party dinner with Ines and friends on Saturday night. Guests brought gifts and the group shared a lot of Italian food. Brad even got a birthday treat with a candle and the group sang happy birthday," says the source.

"He was in the best mood," the source adds. "He sat next to Ines. They were very cute and flirty. You could tell that she makes him happy."

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

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In November, PEOPLE reported 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.

Jewelry executive de Ramon, 32, separated from her husband, Vampire Diaries actor Paul Wesley, earlier this year. She joined Pitt at an afterparty for his new movie Babylon on Thursday, though they did not walk the red carpet together. Afterward, a fashion-industry source close to de Ramon told PEOPLE Pitt "is clearly very into her, given he brought her to his premiere."

Emma McIntyre/WireImage Brad Pitt

"Ines said that Brad is very sweet," the source added, noting that the pair "are planning to spend New Year's Eve together."

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."

Pitt has been married twice — to Jennifer Aniston from 2000 to 2005, then to Angelina Jolie, with whom he shares six kids, from 2014 to 2019. He was most recently linked to Emily Ratajkowski in late September, following the 31-year-old model's split from estranged husband Sebastian Bear-McClard.