AFP

Britain's Queen Elizabeth II joined her great-grandson Prince George at his first birthday party on Tuesday as his parents thanked well-wishers around the world for their warmth and generosity.

Prince William and his wife Kate threw a private bash at their refurbished apartment in London's Kensington's Palace to mark the occasion, with the 88-year-old monarch top of the exclusive guest list that included only royalty, godparents and close friends.

Queen's Elizabeth's green Bentley car was greeted by crowds as it drove through the palace gates.

"We can confirm that the Queen has arrived at Kensington Palace," a royal spokeswoman said.

Kate's parents Michael and Carole Middleton were also seen entering the palace, as was her brother James.

Away from the party, the queen earlier had some private time with George when William and Kate took him to Buckingham Palace.

To mark the prince's birthday, two new photographs of George and his parents were released, showing the toddler fascinated by butterflies during a private visit to London's Natural History Museum.

In a short message accompanying the pictures, William and Kate thanked the public for their good wishes towards the little prince.

"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.

In one of the pictures, George looks about to touch a blue morpho butterfly that has landed on the back of his father's right hand. In the other picture, William, Kate and their son are transfixed by something up in the air ahead of them.

The rare shots of George were taken a few weeks ago during a private visit to the museum's outdoor butterfly exhibition.

"He is very confident on his feet, and very fast," one unnamed onlooker at the shoot told The Daily Telegraph newspaper.

"He is quite determined once he gets going, he didn't want to be stopped. He put his arms out for balance but he wasn't stumbling at all, he is steady on his feet."

Grandfather Prince Charles and his wife Camilla were unable to attend the birthday as they were in Scotland on their annual summer visit.

His Royal Highness Prince George Alexander Louis of Cambridge was born at London's St Mary's Hospital on July 22, 2013, weighing eight pounds and six ounces (3.8 kilogrammes).

William and Kate, both 32, have been hands-on in bringing up their son, bathing him and putting the little prince to bed.

They have revealed that George is a "rascal" who wriggles around a lot and does not want to go to sleep much.

The Duke and Duchess of Cambridge are determined to give George as much of a normal upbringing as they can, keeping him largely out of the spotlight.

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