Stormi, seven.
Kylie showed off her figure in the yellow Chanel two-piece trimmed in black as she let loose during a day on a yacht.
The Kardashians star was also seen cooling off from the heat by taking a shower on board, still managing to look every inch the A-list star.
A clip taken on board the boat showed Kylie and Stormi dancing in matching robes, with their hair wrapped in towels.
Kylie – who also shares son Aire, three, with ex Travis Scott – captioned the sweet post: “Bestie for the integrated life.”
Since flying to Venice for Jeff Bezos and Lauren Sanchez’s wedding, Kylie has been busy exploring Europe.
And when she and sister Kendall, 29, hit the beach in St Tropez earlier this month, fans were shocked to spot a painful-looking scar on Kylie as a result of her breast enhancement surgery .
She previously shared her regrets about having the procedure, saying: “I had beautiful breasts. Just beautiful.
“Perfect size, perfect everything, and I just wish I obviously never made them to begin with.”
Tearing up, she added: “I wish I never did them to begin with. I recommend anyone thinking about it to wait [until] after kids.”
But that didn’t stop Kylie from being refreshingly honest when asked to share details of her recent boob job .
Kylie Jenner Fans Spot ‘Painful’ Plastic Surgery Scar in Rare Unedited Bikini Photos from Her St. Tropez Beach Trip
Taking to Tiktok in June of this year to respond to a fan who asked for more information about the type of surgery she had.
In a rare move, Kylie responded: “445cc, moderate profile, half under muscle!!!!! Silicone!!! Garth Fisher!!! Hope this helps lol.”