The late Princess of Wales’ hairstylist Richard Dalton reveals how the iconic necklace-as-headband moment happened 39 years ago in Melbourne, Australia

Diana, Princess of Wales, wearing a green satin evening dress designed by David and Elizabeth Emanuel and an emerald necklace as a headband, as attends a gala dinner dance at the Southern Cross Hotel on Oct. 31, 1985 in Melbourne, Australia. Photo: Anwar Hussein/Getty

One of Princess Diana’s most memorable fashion moments stemmed, from all places, a sunburn.

As the late Princess of Wales’ hairstylist Richard Dalton wrote in his book It’s All About the Hair: My Decade with Diana, Princess of Wales, he was in Melbourne, Australia with Diana on Oct. 31, 1985 — 39 years ago! — when Diana told him that she “had a bit of a sunburn around her neck from being out in the hot Australian sun all day,” Dalton wrote. (Diana was on tour Down Under with her husband, then-Prince Charles, who coincidentally just wrapped up a tour of Australia and Samoa with Queen Camilla.)

Diana had planned on wearing an emerald and diamond necklace that once belonged to Queen Mary and was a wedding gift to Diana from her mother-in-law Queen Elizabeth to a gala dinner dance at the Southern Cross Hotel that night — a piece that “took my breath away,” Dalton wrote. After hearing about her sunburn, the veteran hairstylist had another idea for how to wear the choker.

Diana, Princess of Wales, wearing a green satin evening dress designed by David and Elizabeth Emanuel and an emerald necklace as a headband, as attends a gala dinner dance at the Southern Cross Hotel on Oct. 31, 1985 in Melbourne, Australia.Anwar Hussein/Getty

“This was a totally spontaneous moment where I thought, ‘What should we do for fun,’ ” Dalton wrote. He added, “I said to Diana, ‘Let’s try something different. Why don’t we stick some emeralds in your hair?’ ”

During the Styling Princess Diana panel at Fotografiska New York celebrating PEOPLE’s 50th anniversary, Dalton explained how it all happened: “I asked Evelyn, her dresser, for six inches of knicker elastic, [the kind used by] grannies,” Dalton said.

He continued to explain his process in his book, which is out now. Dalton fashioned the choker into a headband by tying one end of the knicker elastic to the emerald necklace, draping it across the Princess of Wales’ forehead, pulling it around her head and attaching it in the back to “fit comfortably without falling off, and styled her hair around it,” he wrote. “Diana absolutely loved it, and I never traveled without knicker elastic again.”

Prince Charles, Prince of Wales and Diana, Princess of Wales, wearing a green satin evening dress designed by David and Elizabeth Emanuel and an emerald necklace as a headband, dance together during a gala dinner dance at the Southern Cross Hotel on Oct. 31, 1985 in Melbourne, Australia. Anwar Hussein/Getty

Though he had been working with Princess Diana for years by 1985 — including on her famous tour of Australia with Prince Charles and a nine-month-old Prince William in 1983 — Dalton called the “necklace-as-headband” moment “my first big statement,” he wrote. “And as they say, the rest is history.”

That same evening, Princess Diana wore a cerulean one-shoulder gown by Elizabeth Emanuel, her wedding dress designer, who also spoke at PEOPLE’s Styling Princess Diana panel. Diana worked with the Emanuels — Emanuel and her then-husband, David, who was also her business partner at the time — on not just her July 29, 1981 wedding gown, but on numerous other looks as well, including the satin evening dress worn that night in 1985.

When it came to dressing Diana, Emanuel said she had “No feedback from the palace, nothing, no protocol. I don’t think they expected such a reaction. I think they underestimated the effect of Diana.”

Prince Charles, Prince of Wales and Diana, Princess of Wales, wearing a green satin evening dress designed by David and Elizabeth Emanuel and an emerald necklace as a headband, dance together during a gala dinner dance at the Southern Cross Hotel on Oct. 31, 1985 in Melbourne, Australia.Anwar Hussein/WireImage

Diana, Princess of Wales, wearing a green satin evening dress designed by David and Elizabeth Emanuel and an emerald necklace as a headband, dances during a gala dinner dance at the Southern Cross Hotel on Oct. 31, 1985 in Melbourne, Australia. Anwar Hussein/WireImage

Catherine, Princess of Wales attends The Earthshot Prize 2022 at MGM Music Hall at Fenway on Dec. 2, 2022 in Boston, Massachusetts. Karwai Tang/WireImage

Princess Diana wore the emerald choker — originally a gift to Queen Mary from the Ladies of India in 1911 — many times from 1981 until her death on Aug. 31, 1997, but it hadn’t been seen since her death until Kate Middleton wore it to the Earthshot Prize Awards ceremony in Boston in 2022 — 25 years later. Like her late mother-in-law in Australia in 1985, Kate paired the choker with a bright green dress.

“I love that necklace,” Dalton wrote of the statement piece he repurposed nearly four decades ago. “We caused such a sensation that night.”