The Keeping Up With The Kardashians star - who turned 18 on 10 August - started her morning by sharing a bathroom selfie alongside sister Kendall Jenner, showing the teens in their swimwear as they prepared to hit the beach on the Caribbean island.
Her caption? "We woke up in paradise too."
Sigh. We are so jealous of them being in the sunshine...
The whole Kardashian-Jenner clan - minus Rob Kardashian and Caitlyn Jenner - are currently on holiday in the idyliic setting. Well, a working holiday, anyway, as the E! reality show cameras are also there and have been spied filming the stars all over the island.
Their group got slightly bigger overnight when Kylie was seen collecting rapper beau Tyga, 25, from the St Barts airport. On holiday with the Kylie's mum, sisters and the whole family? Does this mean things are getting serious between the couple?
Kylie and Tyga have been romantically linked since last year and in March their romance seemed to be confirmed when Tyga posted a photo of Kylie to Instagram with the caption: "Certain things capture your eye, but only few capture the heart."
They were seen holding hands in Mexico last week, where Kylie was celebrating her birthday with friends, and Tyga publicly gifted the teen with a new Ferrari for her big day, presenting it to her outside an LA nightclub.
All you need to know about Kylie Jenner: