In a new book, Richard Dalton, who worked with the Princess of Wales for a decade, calls her wedding day hair in 1981 “a disaster”

The Prince and Princess of Wales return to Buckingham Palace by carriage after their wedding on July 29, 1981. Photo: Princess Diana Archive/Getty

If Princess Diana’s former hairdresser Richard Dalton could say anything to his most famous client today, he tells PEOPLE he’d keep it pretty simple: “How do you want your hair done?”

August 31 marked 27 years since the death of Princess Diana following a car crash in Paris at just 36 years old. Though Dalton hadn’t worked with Diana for six years at the time of her passing—having left her employ in 1991 after a decade of service—he always held his memories of her close. Now, with the encouragement of his friend Renae Plant, curator of The Princess Diana Museum, Dalton has shared those memories in his new book with Plant, It’s All About the Hair—My Decade with Diana (out now), offering never-before-told stories about the beloved royal.

“As a loyal subject to the royal family, I never shared anything publicly until now to protect her,” Dalton tells PEOPLE exclusively. “I am 76 years old, [the] same age as [King] Charles, and I wanted to document my real story. [It’s] not a hairdresser’s job to kiss and tell. Now I feel comfortable — 27 years have passed, and nothing in my book is detrimental to Diana’s character. Just wonderful memories.”

Princess Diana wearing an emerald necklace as a headband at a gala in Melbourne, Australia on Oct. 31, 1985. Anwar Hussein/Getty
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Dalton had been responsible for styling Diana’s hair leading up to her wedding to Charles on July 29, 1981, though he wasn’t the one who styled her hair on the big day. That task was handled by his colleague, Kevin Shanley.

In the book, Dalton calls Diana’s wedding day hair “a disaster” — and the bride agreed.

“Diana did express to me that she wished she could do the wedding over again to ‘get the hair right,’ ” Dalton tells PEOPLE. “However, she never mentioned any other regrets while I did her hair.”

The Prince and Princess of Wales on the balcony of Buckingham Palace on their wedding day on July 29, 1981.Terry Fincher/Princess Diana Archive/Getty

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Though he would sometimes only get 15 minutes to style the most famous woman in the world’s hair (and did so everywhere from airplane bathrooms to over the kitchen sink at his own home!), he “never felt pressure,” Dalton tells PEOPLE.

Princess Diana and Dalton loved to push the boundaries with her hair, which had to be styled every which way, including with a myriad of tiaras and hats atop her head that completed her look.

‘It’s All About The Hair – My Decade with HRH Diana Princess of Wales’.The Princess and the Platypus Foundation

“I loved taking risks with Diana’s hair by trying new things like the orchards in Thailand,” he says, referring to his favorite hair moment he ever did for the princess. (Dalton says Diana liked it, too.)

For an event on February 4, 1988, Princess Diana wore a fuschia and purple Catherine Walker dress (which Dalton also wrote in the book was his favorite dress of hers). They were staying at the Imperial Hotel in Bangkok, Dalton writes, “and I literally went around the hotel all day pinching orchids from the floral arrangements to use as accessories in Diana’s hair to match her dress,” according to the book. “Whatever I saw, I took — and nobody stopped me. Eventually, I got all the colors I wanted to use — they represented Thailand and also matched her dress.”

For the event, Dalton styled Diana’s hair in a chignon updo and pinned the flowers to one side of her hair, one by one, he recalls.

“Fresh flowers had never been done before, and she looked sensational that night — and she knew it,” Dalton tells PEOPLE.

Princess Diana wearing a red and purple chiffon evening dress designed by Catherine Walker with silk flowers in her hair, attends a dinner on Feb. 4, 1988 in Bangkok, Thailand.Anwar Hussein/Getty Images

During their decade together, Dalton saw Princess Diana at her best — her witty sense of humor, her dedication to motherhood, her commitment to royal work (“Diana was very conscious that she did not want her hair to overshadow the charity she was representing that day and supporting,” Dalton says). He also saw the former Princess of Wales at her worst, including moments of intensely low self-esteem during the valleys of her marriage to the future King Charles, which ultimately ended in a 1992 separation, the year after Dalton stopped working for her. (Charles and Diana’s divorce was finalized in 1996.)

“Some days she would be happy, some days quiet, some days talkative and some days sad,” Dalton shares in the book. “I experienced all of these with Diana.”

He added that, on her lower days, “sparks would be flying off the hair dryer,” he quips in the book. “I got used to the stress.”

It was only after he stopped working with her in 1991 that Dalton says he realized how much stress he was under as the man responsible for the hair of the most photographed woman in the world.

When he did her hair for the last time, Dalton says she “was going through a really rough stage of her life with Charles and wanted a fresh staff and could tell I wanted my life back,” he tells PEOPLE. “She said, ‘I think [you want] your freedom back’ — and it was mutual. I didn’t realize how much pressure I was under until I left.”

Princess Diana during a visit to Canada on June 27, 1983.Anwar Hussein/Getty

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Much like the 2,700 items in The Princess Diana Museum, Plant tells PEOPLE she saw preserving Dalton’s stockpile of memories as a preservation of history. Plant is also offering a special bonus: a free one-week membership to the Princess Diana Museum for anyone who purchases the book between Aug, 31 and Sept. 7.

“Once these people pass away, their memories are gone forever,” she says, adding “and we know hairdressers are like best friends and get to hear it all.”

It’s All About the Hair—My Decade with Diana is out now.