After one heavy night's partying, Kate - who has taken her nine-year-old daughter Lila Grace on holiday with her - emerged from her five-star, £750-a-night villa soon after 10am and began the day quaffing beer from the comfort of a beachside sun lounger.
"It looked like it was a case of hair of the dog," an onlooker said. "Kate came out of the villa in a scruffy green T-shirt and bikini bottoms and headed to the beach.
"She looked blotchy and worse for wear and knocked back three bottles of beer, which she washed down with Old Jamaica Ginger Beer. She sat smoking with a friend on another sunbed. Her daughter was by her side.
"She had enjoyed quite a big night, which kicked off with a soiree on their private veranda. The party drank three bottles of wine before heading over to the beach for a barbecue.
"They partied for hours and Kate obviously had to sleep it off.
"Sadie was up bright and early to take the kids to breakfast before doing an hour-long yoga session."
Kate and Sadie, who took her 10-year-old daughter Iris on the break, have been staying at a boutique beach hotel where Ian Fleming wrote 14 James Bond adventures. The hotel's luxury villas boast tropical gardens, private swimming pools and outdoor bathtubs. Kate paid extra to have two butlers, two chefs, a housekeeper, a chauffeur, a live-in masseuse and a yoga teacher at their disposal.
According to friends, Kate booked the holiday so that she and husband Jamie, whom she married in the Cotswolds on July 1, could have "a bit of time apart".
"They were getting under each other's feet," says a source.
"Kate has been calling it marriage shock. It's nothing serious, but they agreed a holiday was a good idea. Jamie told her to remember that absence makes the heart grow fonder, and he thinks it will do them good."
Quite what the 42-year-old Kills guitarist will make of his wife's all-night revelling remains to be seen.
Before the summer wedding, Kate's father Peter said he hoped the musician would have a calming effect on his daughter: "We like Jamie, he's a good influence. You've got to calm down at some time and I'm hoping Jamie is a part of that."
The couple were said to be trying for a baby, and Kate was apparently hoping to get pregnant during their honeymoon to the South of France.
But sources at the Caribbean resort say she has been chain-smoking every day of the holiday.
- DAILY MAIL