The Duke of Cambridge participated in the Maserati Royal Charity Polo Trophy at Beaufort Polo Club in Gloucestershire, England, where he was also spotted having some fun with his 3-year-old second cousin, Mia Grace Tindall.
The benefit match helped raise funds and awareness for two charities that William supports as Patron: Child Bereavement UK and Fields in Trust.
During breaks from playing in the match, the 34-year-old royal was seen goofing off with the kids and chasing little Mia around the field. Mia, daughter of Zara and Mike Tindall, is Queen Elizabeth II's great-granddaughter and granddaughter of Princess Anne.
The day before, Prince William was seen taking part in the Colonel's Review -- the rehearsal for Trooping the Colour -- which is the ceremonial event marking the official birthday of Queen Elizabeth II.