In a statement to Woman magazine, the 69-year-old said Meghan and Harry were quick to "trot out the charm when it suits them" but are "otherwise graceless."
The Jamaican-born socialite said Meghan's behaviour showed a "lack of understanding and appreciation" of her royal position.
"I'm not sure who she thinks she is behaving this way," Lady Colin said.
The royal biographer believes the Sussexes are "depriving" royal fans by being "pretentious."
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