The photo also captures a subtle tribute to George's great-grandfather Prince Philip, who died in April this year at age 99.
Prince George appears to be sitting on a Land Rover, which was Prince Philip's favourite car.
The late Duke of Edinburgh even had his casket carried on a custom-made version of the vehicle for his funeral, one that he designed himself.
Prince William and Kate previously revealed that their three children were missing their great-grandfather, in a thank you message sent to fans for the notes of sympathy they received following the passing of Philip.
“They will all miss their much-loved grandfather and great-grandfather, but your message has provided great comfort at this difficult time," the card said.
It comes after William and Kate also paid tribute to the late Duke of Edinburgh recently, where they arrived at a special drive-in cinema in one of his beloved Land Rovers.
"Tonight, with permission from The Queen, The Duke and Duchess attended the drive-in in a Land Rover owned by The Duke of Edinburgh," the royal family shared to Instagram.
"The Land Rover was made in 1966 and is a Series 2A with some modifications. It was used by The Duke of Edinburgh for many years," the caption read.