The Duchess and Duke of Cambridge
09/14/2012 AT 10:45 AM EDT
09/14/2012 AT 08:30 AM EDT
As their goodwill tour of Asia
continues, The Duke
and Duchess of Cambridge
are "saddened," angry and considering legal options as French magazine Closer
published topless photos of Kate on Thursday.
"We certainly feel a red line's been crossed," a palace source tells PEOPLE of the photos, which were taken during William and Kate's private holiday in France
. The source also said that the mood at the palace back home is "one of anger and disbelief."
News of the photos broke as William and Kate – dressed in headscarf – stepped out to visit Malaysia's largest mosque, in central Kuala Lumpur.
A statement from a St. James's Palace spokesman says, "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," the statement continues. "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."
Adding that officials acting on their behalf are considering legal options, the statement says: "The Duke and Duchess remain focused currently on their Tour of Singapore, Malaysia, Solomon Islands and Tuvalu on behalf of HM The Queen."
The couple's next stop is a visit to the rainforests of Borneo.