The two-time Grammy Award nominee, 52, lived it up with Affleck, 48, on Saturday at the nightclub L'Opéra in St. Tropez where they celebrated with an intimate group of friends.
"They are having a beautiful trip," a source tells PEOPLE. "They celebrated Jen's birthday at a club last night. She looked gorgeous and very happy."
The couple got cozy in a booth as they sang along to her 2002 single "Jenny from the Block," which featured Affleck in the music video. They didn't appear to shy away from showing PDA either, as they were surrounded by friends and fans, some of whom posted videos from the festivities to Instagram.
Lopez and Affleck made their rekindled romance Instagram official on Saturday when they shared a passionate kiss in a photo she posted.
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"5 2 … what it do …" she captioned some photos of them celebrating her birthday aboard a yacht. Although her pal Leah Remini previously posted a photo of them at her birthday party, it was the first time the lovebirds shared a glimpse at their relationship on their own social media accounts.
The Gigli stars' romantic yachting trip comes as her ex Alex Rodriguez also posted photos from another boat off St. Tropez, where he's celebrating his own upcoming 46th birthday. "He's with family and friends and people he works with," a source told PEOPLE. "He's doing great and celebrating his birthday and Minnesota Timberwolves sale."
Rodriguez and Lopez called off their engagement in April after four years together. "We have realized we are better as friends and look forward to remaining so," they said in a joint statement to PEOPLE at the time.
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The current couple originally began dating in July 2002 after filming Gigli together. They got engaged that November before postponing their September 2003 wedding, just days before the date, and ultimately calling off their engagement in January 2004.
A source recently told PEOPLE that they are "madly in love" and they are "the loves of each other's lives." Another source added, "Even though their split many years ago was devastating for Jennifer, she has never had a bad word to say about Ben. She believes that it just wasn't meant to be then and feels like they've been given a second chance."