Like most of the pictures of the Cambridge children that are shared with the press, the photo was taken by Kate earlier this weekend at Anmer Hall, the family's home in Norfolk.
Charlotte appears to be standing on a swing in the image, and the photo's background indicates that it's possibly the same swing from a photo the Cambridges shared in June to mark William's 38th birthday.
Charlotte is the second of the royal couple's three children and their only daughter. She was born on May 2, 2015, and named "Charlotte Elizabeth Diana" in tribute to her great-grandmother the Queen and paternal grandmother, Princess Diana.
Last year, Charlotte's birthday images — also taken by her mother — showed the little princess delivering homemade pasta and other food items to high-risk people who were self-isolating because of the coronavirus pandemic.
On Thursday, William and Kate released an intimate family video, featuring the duke and duchess playing with their children, to celebrate their 10th wedding anniversary.