The celebrity magazine 'Closer' printed grainy pictures of 30-year-old Kate, now Duchess of Cambridge, topless at the terrace of a French chateau which were taken during the Royal couple's holiday last week in France, The Sun reported.
The magazine published four photographs of the couple with Kate topless in most of them with a caption 'See...Future Queen of England as you have never seen her...And as you will never see her again'.
The tabloid said that William and Kate were staying in Provence at a chateau owned by Lord Linley, the Queen's nephew, ahead of their Diamond Jubilee tour of Asia-Pacific and were told about the magazine's plan to publish the photos during breakfast in Kuala Lumpur, Malaysia.
Declaring the publishing of the photos as amounting to "crossing the red line" a dismayed St James Palace in a statement described the act by the magazine as "grotesque and totally unjustifiable".
The royal statement likened the publication of the photos to the treatment meted out by media to William's late mother, Diana, Princess of Wales.
"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 statement said.
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"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," it said.
The Sun quoting royal sources said officials acting on behalf of the royal couple are consulting with lawyers to consider what options may be available to them.
It has emerged that British newspapers were offered photographs last week but turned them down.
The printing of photos of topless Kate which comes close on the heels of the splashing of pictures of a naked Prince Harry, Kate's brother-in-law taken in a Las Vegas hotel room last month is likely to cause a major storm, the tabloid said.
The royal couple are touring the globe as part of the Queen's Diamond Jubilee celebrations.
They are on a nine-day trip that started in Singapore. After visiting a mosque in Kuala Lumpur today they are expected to move to the Solomon Islands over the weekend and later Tuvalu.