Kate Middleton and Prince William enjoyed a wild night out in Mustique.

The Duke and Duchess of Cambridge are reportedly in Mustique for the royals' annual break. During their trip, Prince William and Middleton were spotted on a rare night out at the famous Basil's Bar. The theme of the party was a Splash of Gold and the couple was photographed dancing.

According to onlookers, Prince William and Middleton attended "on the early side" of the party and had a great time. They also described the couple as "island chic." The royal dad of three sported a Pinkhouse Mustique shirt to support the local brand.

"They were there for the cocktails segment and kept it rather classy," the source said.

Since the exclusive island offers complete privacy, the Duke and Duchess of Cambridge blend with the tourist. The royal couple was seen dancing with Middleton wearing a headdress and a skirt.

According to reports, Prince William and Middleton travel to Mustique with her parents, Carole and Michael Middleton and their three kids. It is thought that the doting grandparents looked after their grandchildren as the couple enjoyed a night off from their parenting duties.

Meanwhile, according to Martin Katz, he met the royal couple on the same island in 2008 and described them as keen divers. "They're quite the sportsmen. We went diving and they went very deep, more than 90ft. Our instructor said Martin and I weren't qualified to go on the shark dives they went on," he recalled.

During their encounter, the duchess didn't wear any makeup and still looked lovely. He also added that Middleton was gracious and talked to everybody who would talk to her.

"It wasn't like she was working the room, but if someone wanted to speak to her, she was happy to speak. I think what struck me was that they were human like everybody else, dressing to fit in like everybody else," he added.

Prince William and Middleton are bound to return home this week. They are set to reunite with Prince Harry and Meghan Markle on Saturday for Charlie van Straubenzee and Daisy Jenk's wedding. The Duchess of Sussex will also be celebrating her birthday for the first time an official royal on the same day.