The image was taken by her mother Catherine, Princess of Wales, using an iPhone, during a trip to Cumbria earlier this year.

The photograph was put on to the Kensington Palace social media channels with the message: "Happy 10th Birthday Princess Charlotte!" along with a heart emoji.

Charlotte is Prince William and Kate's second child and the third in line to the throne.

Because of changes in 2013 to the rules concerning the order of succession that mean male heirs are no longer prioritised above female heirs, Charlotte, born in 2015, became the first British princess to rank above a younger brother.

The picture taken by her mother, a keen amateur photographer, shows Charlotte wearing a camouflage-style jacket and walking gear.

The names given to the princess - Charlotte Elizabeth Diana - include references to her grandmother Diana and great-grandmother Queen Elizabeth II.

The personal portrait comes just over a week after a similar image was released to mark Prince Louis' seventh birthday. (BBC/ Kensington Palace)