William and Kate have chosen to release the image ahead of their forthcoming tour to Australia and New Zealand which begins next month.

The photograph shows the Cambridges casually dressed as they lean on the sill of an open window at their Kensington Palace apartment.

The couple moved into the property, which had been the home of Princess Margaret, late last year after it had been refurbished.Kate is seated and holds eight-month-old George while William clutches Lupo, a black cocker spaniel.

The couple both smile broadly while their son, who is third-in-line to the throne and will one day be king, seems more interested in the family pet and looks intently to his left at the dog.

Celebrity portrait photographer Jason Bell took the picture and was also the official photographer for George’s christening last October.

Bell is renowned for his images of Hollywood stars and rock and pop legends like Sir Paul McCartney, actress Scarlett Johansson and former England footballer David Beckham.

But he has captured a relaxed image of the Cambridges during the photo session held a few weeks ago.

PA