Touching photographs of William, Kate and Prince George have been released to officially mark the tot's anniversary, as the Cambridges paid their own tribute to the public support they have received.
In a short message the Duke and Duchess said: "We would like to take this opportunity on George's first birthday to thank everyone over the last year, wherever we have met them, both at home and overseas, for their warm and generous good wishes to George and our family."
William, Kate and George were photographed for the official pictures during a visit to the Sensational Butterflies outdoor exhibition at London's Natural History Museum, of which Kate is a patron.
The Prince's blond hair has been swept across his head to create a choir-boy look and he has what his uncle Prince Harry has described as big chubby cheeks and the appearance of a "young Winston Churchill".
One image shows George, who is celebrating his first birthday today, fascinated by a blue morpho butterfly, Morpho peleides, from South America, which has landed on the back of his father's right hand.
The toddler prince, who will one day be king, appears about to pick up the delicate insect as he is sat on a bench with his parents.
Sir Michael Dixon, director of the Natural History Museum, said: 'It was a real pleasure to host our patron and her family earlier this month. They seemed to enjoy their visit, wandering through the tropical plants as brightly coloured butterflies took flight around them.
"It was delightful to see Prince George's first experience of the Natural History Museum and I look forward to welcoming them again in the future."
The Cambridges will celebrate their son's first birthday with close family and friends at Kensington Palace and are expected to hold a birthday party.