A family treat fit for royalty: Mustique may be pricey, but its laid-back glamour, sublime beaches and royal connections give it unrivaled kudos

There are two essential questions you need to ask yourself before booking a holiday to the Caribbean island of Mustique. Am I rich enough? And am I beautiful enough?

At least, that is the general perception. That’s a shame, because as I discovered on a family outing, not everyone was an oligarch and not every woman was ready for the beach. Despite its reputation as a playground of privilege, where rock stars and royals mingle, the island turned out to be more affordable than I thought, albeit in a budget-friendly rather than budget-friendly way.

But with two-bedroom houses available from €12,000 per week, rental prices compare favorably with luxury villas on the Mediterranean in high season.

Our trip was a long-awaited treat. My husband and I were exhausted after a busy year and this break with our children Clemency, seven, and Wilbur, four, felt well-deserved. And besides, I had an important birthday to celebrate.

We stayed at The Cotton House, the island’s main hotel. With only 17 rooms it felt like you were at a house party. That is the point. Mustique is known for being relaxing. I didn’t wear shoes for three days.

Like all buildings on the island, The Cotton House was developed by the late Colin Tennant, later Lord Glenconner. He bought the 1,400-acre island, just three miles long, in 1958 for £45,000. The story goes that he told his wife, Lady Anne, that it would be cheaper to winter there than to heat his country house in Scotland.

Since the land had no running water, jetty or airstrip, he thought he might grow cotton. That all changed two years later when he gave his girlfriend, Princess Margaret, a plot of land for her wedding to Antony Armstrong-Jones. She hired Oliver Messel, the set designer, to build a villa, Les Jolies Eaux, and with it the future of Mustique changed. Cotton went out and celebrities came in.

From then on, the Tennant fiefdom would become one of the most exclusive holiday destinations in the world. It’s not easy to get there. We flew to St. Lucia before boarding an 18-seat Twin Otter for the final leg. Not for the faint of heart; it felt like we were sitting on the pilot’s lap.

Kate stayed at The Cotton House (pictured), the island’s main hotel. “With only 17 rooms, it felt like you were at a house party,” she says

Kate with her husband and children

To develop the island, Tennant formed The Mustique Company, inviting investors to purchase land and build their homes, resulting in the construction of more than 100 homes. Privacy – and the lack of paparazzi – was the big draw for the rich and famous and over the years their numbers grew, including Bryan Adams, Mick Jagger, Tommy Hilfiger and David Bowie.

The Prince and Princess of Wales are regulars, as are Robbie Williams, Tom Ford, Bryan Ferry, Paul McCartney, Bill Gates and the Beckhams. It’s the kind of place where, when you come to the tennis club, you see Tim Henman or Greg Rusedski coaching on the court next door.

Mustique currently has a few hundred inhabitants, which increases to more than a thousand in high season.

One estate, The Terraces, a nine-bedroom hilltop villa with extensive grounds and outbuildings, is on the market for $200 million (the most expensive home in the Caribbean). If you can’t, it can be rented for £150,000 per week.

Of course, none of this stellar history was of any interest to our children. All they wanted was sand between their toes and an endless supply of ice.

Our days fell into a slow rhythm. Lazy breakfast with mango and papaya, walks on the beach and a dip in the hotel pool. I wasn’t so sure about the ocean. What about sharks? It wasn’t until Grant arrived, a affable Australian whose job is to help guests discover marine life, that I took him for a swim around the island.

Below me, in clear water, I saw grouper, angel and parrot fish. Still, I couldn’t stop scanning the waves for fins.

Grant reminded me that I would never see a predator coming: “Too fast.” We struck with steady strokes and soon passed a Balinese-style pavilion high above the water. This was the legendary Basil’s Bar, the island’s social center dating back to 1976 and where the original owner, Basil Charles, still charms customers. We have gotten to know it well.

Legendary: Upstairs is Basil’s Bar, ‘the social center of the island dating back to 1976’

“Mustique deserves this unique journey,” says Kate. Above, the island’s Pink House store

Grant pointed to a blue manta ray and then to five hawksbill turtles calmly munching on seagrass. My eyes were opened to the ocean. When we finished swimming almost two hours later, I saw my husband and children standing on the dock to welcome me home. A moment of utter elation.

Island life turned out to be a simple affair. During the day it was all about our favorite beaches, Macaroni and Gelliceaux Bay. Since no cars are allowed, everyone walks or takes a golf cart, also known as a mule, to reach them. Our children were both safe and happy.

They gathered at The Cotton House jetty and soon joined other young people swimming or snorkeling in an attempt to spot angelfish and eels. Then there were the picnic invitations from other guests on the island. Cricket on the beach for the little ones; sit back with rum punch for us.

Nightlife was just as easy. On Tuesday there were cocktails at The Cotton House; Wednesday ‘Jump Up’ (barbecue and live music) in Basil’s Bar. And there is a relaxed come-in-a-kaftan atmosphere everywhere.

Basil was happy to explain how the island went from jungle and scrub to this side of paradise. He believes the base port and airstrip will keep the mega yachts and private jets at bay.

Hooray for all that. If your goal is to remind yourself what family really means, Mustique deserves that unique journey. But in our case we will do everything we can to make it a trip twice in a lifetime.