In the image, posted on the official Twitter account of the Duke and Duchess of Cambridge, the prince sits beside the duke on the box seat of a carriage while Philip holds the reins and a whip.
The young future king, dressed in shorts and a blue knitted jumper, is smiling and clutching an open book.
Hello! reported that it appears to be a copy of the Tractor Ted book All About Tractors.
The photo of the then two-year-old George was taken in Norfolk by his mother Kate and was accompanied by William’s touching tribute to Philip.
In his message, William said his three children, George, Princess Charlotte and Prince Louis, hold “special” memories of their great-grandfather.
He said: “I will never take for granted the special memories my children will always have of their great-grandpa coming to collect them in his carriage and seeing for themselves his infectious sense of adventure as well as his mischievous sense of humour!”
William’s brother, the Duke of Sussex, also paid fond tribute to Philip and said he will be “always remembered” by his great-grandson Archie Mountbatten-Windsor and his unborn great-granddaughter.
Harry, who has returned to the UK for the funeral, said: “You will be sorely missed, but always remembered – by the nation and the world. Meghan, Archie and I (as well as your future great-granddaughter) will always hold a special place for you in our hearts.”
The Duchess of Sussex, who is due to give birth to the couple’s second child in the summer, remains in California after she was not given medical clearance by her doctor to travel.