Prince William and his wife Kate released a picture of their daughter Charlotte to mark the princess's ninth birthday on Thursday.

In the photograph taken in the last few days by her mother, the Princess of Wales, Charlotte, the couple's second child, was pictured smiling happily in the garden of their home in Windsor.

"Happy 9th Birthday, Princess Charlotte!" a message on the couple's X account said. "Thank you for all of the kind messages today."

It has become tradition for Kensington Palace to release pictures taken by Kate, a keen amateur photographer, to mark birthdays and other family occasions.

However, a picture issued this year on Mother's Day in March was withdrawn by a number of news organisations, including Reuters, because it had been edited, something for which Kate later apologised.

That occurred shortly before the princess revealed she was having preventative chemotherapy after tests carried out in the wake major abdominal surgery she underwent in January revealed that cancer had been present.

Heir to the throne William resumed official duties last month, but Kate will only return to the public spotlight when her medical team say she is well enough to do so.

King Charles returned to public-facing engagements this week for the first time since he was diagnosed with cancer in February.