Kate has not been seen since late December, when she was pictured on a Christmas Day walk with other members of the Royal Family in Sandringham, Norfolk.

The 42-year-old future queen was admitted to the London Clinic - the private hospital where the King underwent treatment for an enlarged prostate - for a planned operation on 16 January.

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Now US celebrity news site TMZ has published a picture of the princess which it says was taken near Windsor Castle on Monday.

Kate wore dark sunglasses and sat in the passenger seat of a black Audi which was being driven by her mother, Carole Middleton.

The photo is understood to have been taken by unauthorised paparazzi.

It comes as Kate's uncle Gary Goldsmith entered the Celebrity Big Brother house on Monday night.

The 58-year-old businessman, and younger brother of Kate's mother, Carole, was asked by the show's host AJ Odudu if the princess will be watching.

He replied: "If she is it will be behind a sofa, I guess."

The princess returned home from hospital after 13 days, and Kensington Palace said at the time the princess was "making good progress".

Kate is not expected to return to official royal duties until after Easter.

Charles, 75, visited his daughter-in-law's bedside after being admitted himself to the London Clinic on 26 January for treatment for an enlarged prostate.

It was announced just under a fortnight later that he had been diagnosed with cancer.

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Kate was also visited by her husband, the Prince of Wales, who temporarily stepped back from his royal role to juggle caring for her and their children.

In early February, Prince William carried out his first public engagements since her surgery.

Details of the princess's condition have not been revealed but the palace said it was not cancer-related and that Kate wished her personal medical information to remain private.