William and Kate are suing Closer after the French magazine recently published photographs of the duke and duchess of Cambridge sunbathing in southern France last month. Several newspapers have since run the images, as well.
"I have been there and know what it's like," Ferguson, who is William's 52-year-old aunt, told London's Daily Mail newspaper. "Everyone is entitled to privacy. It is a devastating invasion of one's personal inner space. It is deplorable, abhorrent and despicable."
Ferguson was referring to how embarrassing topless photos of her with American businessman John Bryan surfaced in 1992, shortly after she and her husband, Prince Andrew, broke up.
"She is a beautiful young woman doing a great job for the country," Ferguson said of Middleton."Why should she be stripped of that moment with her husband?"