The photo of the royal couple’s second child and only girl was taken by her mother, Kate Middleton, who is a prolific photographer, in Norfolk.
Charlotte flashes her pearly whites in the sweet photo as she enjoys the outdoors in a pretty pink and blue floral summer dress.
Many Twitter users noted the girl’s resemblance to her father.
Others noticed how much she looks like her late grandmother Princess Diana.
The duchess and Prince William also celebrated their tenth wedding anniversary last week.
William and Kate also have two boys: Prince George, 7, and Prince Louis, 3.
The couple released a cute snap of Louis on a bicycle for his third birthday on April 23. The picture was taken before his first day of nursery school.
The family will likely be an Anmer Hall at Queen Elizabeth’s Sandringham in Norfolk this weekend because Monday is a public holiday in the U.K, according to People magazine.
The Associated Press contributed to this report.