A furious Duke and Duchess of Cambridge launched legal action against a French magazine tonight after it published topless pictures of Kate taken while the couple were on holiday.
The publication was compared by St James's Palace to the worst experiences of Diana, Princess of Wales at the hands of the paparazzi.
The palace led a chorus of protests, describing the invasion of privacy as "grotesque and totally unjustifiable".
Royal aides drew parallels between Diana's most upsetting encounters with certain elements of the press and the "unthinkable" actions of the French magazine Closer, which left Kate and William feeling "anger and disbelief". And the palace has now announced that lawyers would be pursuing the matter through the French courts.
In a short statement, the palace said: "St James's Palace confirms that legal proceedings for breach of privacy have been commenced today in France by the Duke and Duchess of Cambridge against the publishers of Closer Magazine France."
The royal couple have the sympathy of Downing Street with a source close to David Cameron saying that Number 10 "echoes the sadness of the palace" over the publication of the pictures.
In a strongly-worded statement 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, let alone publish them. Officials acting on behalf of their Royal Highnesses are consulting with lawyers to consider what options may be available to the Duke and Duchess."
But Laurence Pieau, the editor of Closer, was unrepentant, defending her decision to publish the pictures during an interview with the French radio station Europe 1, insisting there was "nothing degrading" about the photographs and claiming she could not understand the couple's reaction.
Ms Pieau also told the AFP news agency: "These photos are not in the least shocking. They show a young woman sunbathing topless, like the millions of women you see on beaches."