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Meanwhile Leo, who most recently dated model Nina Agdal, stripped down to his swimming trunks, slung low at his hips to ensure he made the most of the glorious sunshine.
Kate and Leo were in St Tropez for Leo's annual foundation gala held at the Domaine Bertaud Belieu, where the pair auctioned off the chance to dine with them at the winner's place of choice in New York City.
Kate slipped into a florescent orange bikini for the rendezvous, which she paired with a sheer white beach dress, to accentuate her enviable womanly curves.
Keeping casual ahead of their glamorous evening, the mum-of-three added a selection of delicate gold necklaces and tied her look together with oversized dark sunglasses.
Cosying up together at the bash, the actor, 51, playfully joked in the caption: 'Gangs all here. Go figure...'Still looking good: Adding a gold necklace of his own, the star kept casual as he spent a day relaxing with Kate - with his hair swept naturally to the side, proving him to be as handsome as his younger Titanic days (R) two decades later Close: The pair later attended Leo's foundation charity gala that night (above) - with Leo in a slick suit and Kate in a slinky black dress - where they auctioned off an intimate dinner with them in NYC as the top fundraising prize Kate and Leo both rocketed to super-stardom after playing star-crossed lovers Rose De Witt Bukater and Jack Dawson in the 1997 classic Titanic - and have remained close ever since.
In the film, Winslet's character leaves fiance Cal Hockley (played by Zane) after meeting scrappy, working class artist Jack and falling for him, while aboard the doomed luxury liner.
'The best': The pair have been very open with their friendship in the past - with Kate gushing in her Golden Globes speech in 2009: 'Leo, I'm so happy I can stand here and tell you how much I love you and how much I've loved you for 13 years'Kate bagged the Best Actress gong at the 2009 Golden Globes for the flick, and her speech went down in history with fans as she openly thanked Leo for both his co-operation on screen, and strong friendship.