A fellow vacationer tells PEOPLE he found a memorable way to break the ice when he met the royal couple on the island a few years ago

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When it comes to private getaways, Prince William and Princess Kate look no further than the resort island of Mustique.

The idyllic Caribbean destination has been a favorite of the royal couple for years. They first visited the island together when they were dating in 2008 and have since spent many family vacations there – including two babymoons!

On previous visits, William, 33, and Kate, 33, stayed at the Aurora House, and when they’re not lounging by the pool, the royal couple’s choice of activities include scuba and snorkeling, tennis, horseback riding and a Tuesday night cocktail party at the Cotton House Hotel.

Fellow traveler Martin Katz, a famed Beverly Hills jeweler and celeb favorite who designed Kim Kardashian’s wedding-day earrings, met the royals when he was vacationing on the island with his wife Kelly in May 2008.

“I was standing at the [hotel] bar ordering one of the fancy drinks and Kate actually came up to the bar and was quite pleasant and chatty. She couldn’t be more friendly and more open,” Katz tells PEOPLE.

While Katz chatted with Kate, his wife talked to Prince William – until Katz found a memorable way to break the ice.

“We started talking about scuba diving. They had gone that day or the day before, and while I was talking, I was holding a glass of fruit punch and it slipped from my hand and crashed to the floor and sprayed all over the prince’s feet. He was in flip-flops.

“I was mortified of course, but all I heard was, ‘That was quite refreshing, thank you.’ His mother would have been quite proud that he handled himself with such dignity. It was a very embarrassing moment for me, and he was very kind about it, and my wife never lets me forget that moment. I tried [to buy him a round], but I don’t think he was partaking in any more rounds,” he says.

For those who treasure their privacy, like William and Kate, Mustique is a perfect place to vacation. There is a no-fly zone over the island. The beaches, while public, can only be seen by non-residents from the sea and the locals know just about everyone who might venture onto the island.

“They had a wonderful villa that overlooked a very quiet beach,” Katz says. “It is a very simple life. We saw them up by their villa and occasionally on the beach. They were pretty much allowed to be left alone.”

With the absence of cameras, the princess is able to let her hair down and relax.

“Kate looked very casual, she wasn’t particularly wearing makeup, she looked lovely. She just couldn’t be more 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.

“They were lovely and they couldn’t be more present,” Katz says. “I think what struck me was that they were human like everybody else, dressing to fit in like everybody else.”

In February, Will and Kate took a trip to Mustique alongside her family.

Pictures of the exclusive Caribbean island showed William relaxing after a swim, as sister-in-law Pippa Middleton, 31, and brother-in-law James Middleton, 27, looked on. Kate, who was pregnant with Princess Charlotte at the time, strolled with Prince George and nanny Maria Borrallo.

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Reporting by Christine Pelisek