The Associated Press (AP) has told Sky News the photo shows an "inconsistency in the alignment of Princess Charlotte's left hand".

The picture in question was released on Sunday morning to celebrate Mother's Day and shows Kate surrounded by her and Prince William's three children: Prince George, Princess Charlotte and Prince Louis.

The image was initially circulated by a number of picture agencies but on Sunday night at least two withdrew it and told media outlets to "kill" the photo from their systems and archives.

AP told Sky News in a statement: "The Associated Press initially published the photo, which was issued by Kensington Palace. The AP later retracted the image because at closer inspection, it appears that the source had manipulated the image in a way that did not meet AP's photo standards.

"The photo shows an inconsistency in the alignment of Princess Charlotte's left hand."

Kensington Palace had provided the photo to agencies and said it had been taken by the Prince of Wales earlier this week.

Kensington Palace has declined to comment.

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In a message accompanying the photo on Instagram, Kate wrote: "Thank you for your kind wishes and continued support over the last two months.

"Wishing everyone a Happy Mother's Day."

The Prince and Princess of Wales's Instagram post featuring the image has not been taken down.

The picture and message came amid speculation about Kate's health following a brief hospital stay in January.

Kate was admitted for planned abdominal surgery on 16 January, exactly a week after her 42nd birthday.

The following day, the Palace said the operation was successful and Kate stayed in hospital until 29 January, when she was discharged home to Windsor.

At the time, Sky News understood that her recuperation would likely take between two and three months.

Kate has not been seen in public since she joined other members of the Royal Family for a Christmas Day walk, though US celebrity news site TMZ published a photo of her on 4 March.

The photo was understood to have been taken by unauthorised paparazzi near Windsor Castle.

William has been attending events and engagements solo while Kate has been recuperating.