Princess Charlotte’s ninth birthday has been marked by the release of a picture showing the young royal looking relaxed and smiling.

The Prince and Princess of Wales’ daughter was pictured casually posing outside, at an undisclosed location in Windsor, next to a clematis plant with pink petals, in the image taken by Kate.

Charlotte’s big day comes as the Wales family navigate Kate’s cancer treatment, with the princess away from official duties since the start of the year.

The photograph was posted on the royal couple’s official X account, formerly known as Twitter, with the words “Happy 9th Birthday, Princess Charlotte!” and a cake emoji.

It also said: “Thank you for all the kind messages today.”

Charlotte and her siblings, Princes George and Louis, have been the focus for the William and Kate as the princess receives treatment for an undisclosed form of cancer.

Kate said in her video message to the nation announcing her diagnosis that she and William “have been doing everything we can to process and manage this privately for the sake of our young family”.

Third in line to the throne Charlotte attends the co-educational private Lambrook School near Ascot in Berkshire, and loves dancing, especially ballet and tap.

William recently revealed what tickles his daughter, during a visit to a school in the West Midlands where he was asked to contribute a “dad joke” to a student radio broadcast.

In his pre-recorded piece William told the listeners: “I think what I’ll do, is I’ll say a joke which is Charlotte’s favourite joke at the moment, she keeps telling me.”

William said “Knock Knock” and when the pupils said “who’s there” the royal replied “Interrupting cow” and as the group tried to say “interrupting cow who?” he made them laugh by saying “Mooo”.

Charlotte has a reputation for being feisty compared with her older brother George, and Kate has described the princess as “the one in charge”.

The youngster was spotted reminding George to bow to the coffin of their late great-grandmother the Queen at her state funeral, and she kept Louis in check during a Trooping the Colour by placing her hand over his hand to calm his over-enthusiastic waving to the crowds from the carriage.

This time last year, Charlotte was preparing for her grandfather the King’s coronation, where she processed through Westminster Abbey hand in hand with Louis.

The young princess was last seen in public on Christmas Day when she walked to church with her family and second cousin Mia Tindall at Sandringham.

William and Kate released the new image of Charlotte straight to social media, rather than under embargo to the press as was the tradition, just as they had done with the picture marking Louis’ sixth birthday on April 23.

The change follows the uproar sparked by the princess’s digitally altered Mother’s Day photo.