In a new book, Richard Dalton talks about styling the former Princess of Wales’ hair for a decade — and giving both of her sons their first haircuts

Prince Harry and his mother, Princess Diana.

Princess Diana’s longtime hairstylist Richard Dalton was in charge of styling the most famous woman in the world’s hair for a decade, but she wasn’t his only royal client.

For the then-Wales family — Princess Diana, the future King Charles, and their sons, Prince William and Prince Harry — hairstyling was a true family affair with Richard Dalton.

He tells PEOPLE he is responsible for both William and Harry’s first haircuts and held that responsibility “up until they were 10 and 7.”

It’s an anecdote Dalton details in the new book It’s All About the Hair — My Decade with Diana, which he collaborated on with his friend Renae Plant, curator of The Princess Diana Museum.

“The first time I cut Harry’s hair, the windows were open, and I was holding his lock of reddish hair, thinking, ‘Oh, if this blows away, I’m in trouble. I’ll be put in the Tower of London,’” he tells PEOPLE exclusively. It didn’t, and Diana placed it in her baby books, Dalton writes in the book.

Princess Diana, Prince William and Prince Harry at the piano in Kensington Palace.Tim Graham Photo Library/Getty

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Of the brothers, “They were so sweet, the boys,” Dalton says in the book. “I would cut their hair in their nursery. Every time they saw me coming into the nursery, William would get terribly excited. He’d run and get the little white chair and would put it on top of the square coffee table. They would sit in the chair and watch television while I cut their hair.”

Dalton adds, “They always knew they got ‘extra’ TV when we had haircuts, so they thought it was great.”

Prince William, Princess Diana and Prince Harry at the Heads of State VE Remembrance Service in Hyde Park on May 7, 1995.Anwar Hussein/Getty

After Princess Diana recommended it, “I cut Prince Charles’ hair on occasion,” Dalton tells PEOPLE. In the book, Dalton remembers Diana telling him, “Please just do it and do something with it,” adding that she “wanted me to fix it and make it a little more modern.”

Dalton would see Prince Charles when he popped into his then-wife’s dressing room from time to time. “I think Charles was reserved, as he was brought up with an understanding of how to behave in front of staff,” Dalton writes. “He was very nice, but you would not see him express himself openly or passionately.”

Not so for the former Princess of Wales. “Diana was a woman in love,” Dalton writes

In his book, Dalton shares that the most significant transformation he observed in Diana was when she became a mother—a journey he was privileged to witness from the beginning, having worked with her even before her July 29, 1981, wedding to the then Prince of Wales. Dalton recalls how Diana truly blossomed with the births of William in 1982 and Harry in 1984.

Princess Diana, Prince Harry, Prince Charles and Prince William leaving Italy on the royal yacht Brittania in April 1985.Diana Archive/Getty

“She absolutely loved and adored her boys, and she also craved affection,” Dalton shares in the book. “Her boys gave her that. The princess was at her very best as a mother.”

Dalton writes of the “great memories” of the boys always wanting to be around their mother — “and under my feet when I was trying to do her hair,” he shares.

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

Preserving Diana’s legacy is why Plant created The Princess Diana Museum and why she encouraged Dalton to share his memories.

“Diana will one day soon become the king’s mother when William becomes king, and I hope that the work I have done will inspire future generations to understand who Diana really was,” Plant tells PEOPLE.

She adds, “It’s just so sad that we never got to see her become a grandmother, and I always imagine what she would be doing today if she were alive.”

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Princess Diana in Hong Kong, Nov. 8, 1989.Kent Gavin/Daily Mirror/Mirrorpix/Getty

For a limited time, Plant is 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.

“I decided to create the Princess Diana Museum to honor her incredible life and legacy,” Plant says. “I never imagined it would grow this big — housing the largest private collection in the world with over 2,700 items.”