updated 06/18/2012 AT 12:00 PM ET
•originally published 06/18/2012 AT 1:50 PM ET
Wearing the traditional plumed hat and long, deep purple velvet robe, he walked down from Windsor Castle to the service alongside his father Prince Charles as his wife smiled at him outside of St. George’s Chapel.
Kate, Duchess of Cambridge, in an Alexander McQueen coat and hat by Jane Corbett, was with Charles’s wife Camilla, Duchess of Cornwall, Sophie Wessex and other royal relatives watching the procession from the Galilee Porch.
They watched as the Duke of Edinburgh, 91, walked the close to half a mile distance down before everyone curtsied to Queen Elizabeth, 86, on his right.
Camilla, meanwhile, kept everyone laughing as they waited for the knights to pass.
The annual service to celebrate the U.K.’s most ancient order of knights has been a regular fixture in the royal calendar for William since he became a member four years ago.
At the end of the hour-long service, Kate and William shared a carriage ride back up the hill inside the castle grounds with Charles and Camilla.