The 39-year-old royal spent Father's Day with his two eldest kids at an official event.
The trio visited the Sandringham Estate in Norfolk, England, on Sunday, to kick off a local half marathon.
George and Charlotte matched in navy shorts, with the young prince wearing a plaid button-down shirt while his sister sported a pastel pink polo sweater.
Their proud dad invited his children to kick off the race, as they all counted down in the microphone together.
In addition to Father's Day, the Duke of Cambridge, who is also dad to 3-year-old son Louis, celebrated his 39th birthday on Monday.
His father, Prince Charles, marked the occasion with a sweet throwback photo of himself holding William as a baby.
"Wishing The Duke of Cambridge a very Happy Birthday today! 🎂" the Clarence House account captioned the image.
The Royal Family account, which represents Queen Elizabeth II, also shared a sweet family photo of William with Kate and their three children at a past Trooping the Colour parade.
"Wishing the Duke of Cambridge a very happy birthday today!" read the caption.
For more from the royals, watch the clip below.