Ever since his debut on the steps of the Lindo Wing, Prince George has been the apple of royal watchers' eyes. Now, as the Duke and Duchess of Cambridge's firstborn turns five on July 22, his family is celebrating by treating fans to a new photo of the future king one day before his birthday. Kensington Palace shared the adorable snapshot of the almost-five-year-old beaming as he stands against what appears to be the red brick of St. Jame's Palace.

Prince George looked so sweet in his fifth birthday portrait! Photo: © Matt Porteous

In the photo, George shows off his megawatt smile, wearing the same outfit he donned for Prince Louis' christening – a white Amaia Kids shirt with blue piping and navy shorts, his blond hair styled in a sweet side part. The third-in-line to the throne looks up with his big brown eyes, likely at the photographer – or maybe his parents, Prince William and Duchess Kate, who could very well be making funny faces behind the camera to make him smile!

GALLERY: Prince George's cutest photos

Princess Charlotte and Prince Louis' big brother is likely to mark his latest milestone with a weekend of family festivities. While the Cambridges have thrown small, private parties in the past, they're believed to be on their annual vacation in Mustique with the Middletons – so George may be celebrating in the sun! Back home, fans can toast his big day with the Royal Mint's latest £5 coin, which features the legend of St George and the Dragon and the year 2018 in honour of the future monarch.

Prince George posed with his dad on the steps of Thomas's Battersea Day School. Photo: © Chris Jackson/Getty Images

This has been a big year for the little prince, who looked happy as ever as he attended his first day of school at Thomas's Battersea in September 2017. The outing resulted in a series of adorable photos with his doting dad.

Now officially on his first summer break from school, George will get to spend the season playing in the sunshine with his new brother Louis and sister Charlotte, with whom he's already gotten in some major fun! The duo was photographed playing with a slinky and frolicking on the grass while watching dad play in the Maserati Royal Charity Polo Trophy from the sidelines with mom Kate!

Charlotte and George ran through the grass at the polo match. Photo: © Samir Hussein/WireImage