Meghan Markle's "graceless" behaviour would have "appalled" the late Princess Diana, claims royal biographer Lady Colin Campbell.
The author who has published three books about the British Royal Family and claim to have been a close confidante of Diana, says Harry and Meghan "trot out the charm when it suits them" but are "otherwise graceless".
"Diana would be appalled, she had enough nous to know when to put on a show," the 69-year-old told the UK's Woman's Magazine.
"She was very aware of how important it was to be gracious, while Meghan - and Harry to an extent - trot out the charm when it suits them, but otherwise are graceless."
She also criticised the Duchess of Sussex for showing a "lack of understanding and appreciation" of her royal position - and says that she and Harry are "depriving" royal fans by being "pretentious".
"Her behaviour shows a lack of understanding and appreciation of what being royal is. I'm not sure who she thinks she is behaving this way."
Campbell issued a word of warning to the new royal.
"I have an awful feeling that Meghan needs to understand things she doesn't yet understand. There is a massive difference between being a celebrity, hustling your way from the bottom to the top, and being a royal."
"She's an actress, she needs to come up with a new act!"
Last month the author slammed Markle for "acting like a celebrity" by guest-editing the September issue of Vogue.
"She was never an A-lister, so she needs to stop acting like one," she told Closer magazine.
"Royalty do not behave like celebrities do. It's cheap, vulgar and irresponsible."