The Queen joined grandchildren Prince Harry and Zara Phillips, Zara's husband Mike Tindall and Kate's childhood pal Emilia d'Erlanger at the Peter Rabbit themed bash.
According to reports, the do was organised by Kate's mum Carole Middleton - which made perfect sense seeing as she runs her own kids party planning company - with a huge cake specially made by the royal baby's Spanish nanny Maria Teresa Turrion Borrallo.
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While the soiree saw a good turn out with Kate's brother and sister James and Pippa arriving a little later on, grandparents Prince Charles and Camilla the Duchess of Cornwall were notably absent, but they made sure to buy little George a present.
The party followed the release of a new set of official images of baby George. The images saw the young royal meeting a butterfly while on a visit to the Natural History Museum in London with his parents.
The photos came with a statement from the Duke and Duchess of Cambridge thanking members of the public for the hundreds of presents, cards and letters of good wishes they have received since their son's birth last July.
"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," they said.