Sam McKnight, the hairdresser who once styled Princess Diana, condemned what he described as "evil" and "nasty" comments aimed at the Princess of Wales after the royal debuted noticeably lighter hair upon returning to public duties.

The Princess of Wales, 43, resumed engagements this week following a summer break that reportedly included a family yacht trip to Greece. On her first public appearance since the break she appeared with brighter, blonder locks, prompting a mix of reaction online, including negative and abusive remarks directed at her appearance.

McKnight, 70, posted on Instagram that he was "shocked, horrified, dismayed and disgusted" by the response. "A woman's hair is very personal to her," he wrote. "It's armor, defence, confidence and so much more."

The stylist, who was once the personal hairdresser to the late Diana, Princess of Wales, added that he was particularly disturbed by the source of many comments. "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," he wrote.

McKnight also defended the princess's public service, saying, "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."

Online commentary about the appearance of members of the royal family is a recurring phenomenon. Female royals in particular have regularly faced intense scrutiny over clothing and hairstyles, which can attract widespread attention and commentary on social platforms.

The Instagram post by McKnight underscores how those close to public figures sometimes speak out against online abuse. He did not elaborate on when or by whom the princess's new hair was styled, nor did his post address any broader plans for her public schedule.

Representatives for the Princess of Wales did not immediately respond to a request for comment. The debate over online criticism of public figures has continued to draw attention from mental health advocates, media organizations and public figures themselves, as platforms and audiences consider the impact of sustained scrutiny on individuals in the public eye.