Theroux -- who called it quits with estranged wife Jennifer Aniston in February -- was all smiles as he and the 28-year-old Spider-Man: Homecoming star spent time hanging out together in the ocean on May 26.
The 46-year-old Leftovers star rocked a pair of blue-and-white swim trunks and a gold necklace while the gorgeous Harrier showed off her svelte physique in a vermillion one-piece bathing suit and a pair of round-rimmed shades.
The two spent much of their time lounging around on a floating dock in the middle of the ocean before showing off their daring side by leaping off a hanging rope ladder into the clear waters, as well as jumping off a diving board.
“Justin is not in a relationship,” a source tells ET. “He’s super social and loves meeting new people and collaborating on ideas with friends. These days he’s been spending time with friends and family – he’s super close with his brother."
While Harrier was recently in France for the Cannes Film Festival -- where she was promoting her upcoming film, BlacKkKlansman -- she and Theroux were both in the luxury vacation destination this weekend for the Louis Vuitton Cruise 2019 fashion show.
Justin Theroux Breaks Social Media Silence Following Jennifer Aniston Split With Surprising Post
The star-studded runway show was held in the small hilltop village of Saint-Paul-de-Vence, and featured a score of big name guests, including Emma Stone, Ruth Negga and Jennifer Connelly, among many others. Theroux is currently one of the faces of Louis Vuitton's spring campaign.