This claim was made by Elizabeth Holmes, the author of the book, HRH: So many thoughts on the royal style.
She said People magazine, “For Charles, you can tell in his public remarks, fashion is one of the things he sought to use against it. [He used Diana’s] interest in fashion, and interest in its fashion, to paint it as superficial or frivolous. What an outdated and unhappy line of criticism, especially because these women use their clothes so wisely.
During one of their engagements in the Gulf States in 1989, Prince Charles insulted Princess Diana right in front of other dignitaries according to The Chronicles of Diana by Tina Brown.
At the time, the princess was asked about the type of arrangements she made for mentally disabled children while on tour. However, before he could respond, the prince rang the bell saying, “Shopping, right, honey?”
According to Princess Diana’s private secretary, Patrick Jephson, “the words have fallen into the stillness of marble like bricks into flat glass”.
At the time, [Diana] colorful, muttered something inaudible and fell silent.