Mustique is a Caribbean island that lies between Barbados and St Lucia. It’s a hedonistic island where the affluent and famous have been flocking since the 1960s because it promised a press-free zone.

Princess Margaret, according to the Channel 5 documentary The Royals on Holiday, was the one who initially fell in love with the island.

“Colin Tennant offered her a plot of land as a wedding present and she said, ‘Thank you very much, yes I’d like that,’” said Richard Kay, editor-at-large at the Daily Mail, in the documentary.

“They literally marked it out with their feet and Margaret said: ‘Well I’d like a bit more.’ So she sort of kicked the sand a bit further and it got a bit larger and he went along with that.

“It became a real refuge for Princess Margaret.”

According to royal commentator Claudia Joseph, the island developed a reputation over time.

“It gained a reputation over the years as being quite a hedonistic island,” she explained.

Princess Margaret was photographed with Roddy Llewellyn on the holiday (Image: Getty Images)

“Margaret owned a house called Les Jolies Eaux and she used to entertain lavishly.

“They used to stay up until all hours partying and having fun.

“She wasn’t particularly suited to royal life with all of its rules and regulations and protocols.

“She enjoyed the privilege and the things it afforded her, but those restrictions really were quite damaging to her, I think, and for a large part of her life she wasn’t all that happy in the Royal Family.

“Mustique was that place she could go and let off steam, enjoy everything about life and not have to worry.”

“They were not just candid photos of Margaret on holiday. These pictures would have major repercussions,” the documentary says.

“Even though they thought they were away from the cameras, the News of the World managed to grab a photo of her on the beach with Roddy Llewellyn and obviously it went around the world,” Ms Joseph added.

Mr Kay added: “It was that trip to the Caribbean where the wider world found out she was conducting an affair with him.”