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A French magazine has stoked controversy by publishing pictures of Catherine, the Duchess of Cambridge, topless while on vacation with Prince William, prompting the threat of legal action from palace officials over what they blasted as a "grotesque" invasion of privacy.french photographer pics jewels amazing body sexy The pictures were taken while the couple was staying at a private chateau in Provence, in southern France, according to Closer magazine. A spokesman for St. James's Palace told CNN the photos appeared to be genuine. "We believe a red line has been crossed. We are communicating with French lawyers," he said. A royal source told CNN the Duchess of Cambridge is "upset" by the claims in the French magazine. The photographs, which are grainy and appear to have been taken with a long lens, cannot be accessed on the website of Closer in France, which shows only the magazine's front cover with heavily blurred-out images. A statement from St. James's Palace said: "Their Royal Highnesses have been hugely saddened to learn that a French publication and a photographer have invaded their privacy in such a grotesque and totally unjustifiable manner. "The incident is reminiscent of the worst excesses of the press and paparazzi during the life of Diana, Princess of Wales, and all the more upsetting to The Duke and Duchess for being so. "Their Royal Highnesses had every expectation of privacy in the remote house. It is unthinkable that anyone should take such photographs <b>...</b>