Princess Diana‘s former hairstylist is weighing in on Kate Middleton‘s headline-making new look.

Princess Kate and Prince William, both 43, visited the Natural History Museum’s newly transformed gardens on Thursday, Sept. 4 in their first joint outing following summer break. While the visit included an educational tour, meetings with local schoolchildren and even an unexpected downpour, the standout moment was the debut of Kate’s new hairstyle.

After hints of a hair transformation during a brief appearance in August, Thursday’s outing confirmed that the Princess of Wales is now sporting lengthy, highlighted tresses — her blondest and longest style ever.

The change prompted a wide range of commentary online, including from hairstylist-to-the-stars Sam McKnight, who served as Princess Diana’s personal hairstylist from 1990 until her tragic death in 1997.

In a strongly-worded post on Instagram, McKnight called out anyone criticizing Kate’s look.

“I am shocked, horrified, dismayed and disgusted by all the nasty comments about the Princess of Wales today,” he wrote. “A woman’s hair is very personal to her, it’s armour, defence, confidence and so much more.”

“I cannot believe how evil and lacking in any kind of empathy are the comments, the majority made apparently by other women, attacking a vulnerable other young woman, who has no choice, by dint of who she married, and the role she took on, to bravely face the public,” McKnight continued.

McKnight also referenced Princess Kate’s cancer treatment and recovery in his message.

“I’m sure she would rather be away from the public arena. She has brilliantly and quietly, unselfishly represented our country, the soft power we still have as a nation. Cancer affects individuals differently, but is life-changing for everyone. So FFS LEAVE HER ALONE. SHAME ON YOU,” he wrote.

In March 2024, Kate revealed she was undergoing cancer treatment, and in January 2025, she shared with “relief” that she is now in remission.

During a royal visit to a local hospital earlier this year, Princess Kate opened up about her experience, telling a patient that she “didn’t have to have” cold cap therapy, a treatment that helps reduce the risk of hair loss, during her cancer treatment.

McKnight and Princess Diana first met during a shoot for British Vogue, after which the stylist inspired what would become the princess’s signature short cut.

In 2021, after helping to recreate the look for The Crown, McKnight recalled how he played around with the princess’s hair during the shoot. “I made it look short under the tiara — I faked it a bit,” he said.

Can’t get enough of PEOPLE’s Royals coverage? Sign up for our free Royals newsletter to get the latest updates on Kate Middleton, Meghan Markle and more!

When they wrapped, McKnight said, Diana asked how he would do her hair if she let him do whatever he wanted.

“I said, ‘I would cut it all off and just start again,’ ” he recalled. “It was the beginning of the ’90s, and it was at the time that I was doing lots of shows and covers and a lot of the girls had short hair, and we were moving from the big frou-frou ’80s into the sharp, more androgynous, business chic of the ’90s.”

In a surprising move, she said, ” ‘Well, why don’t you just cut it off now?’ So I cut it off then, and we never looked back,” McKnight shared.