William, Philip, Queen and Kate Attend Garter Day Celebrations

Highest honour Queen can bestow

WINDSOR, ENGLAND - JUNE 18: A general view during the annual Order of the Garter Service at St George's Chapel, Windsor Castle on June 18, 2011 in Windsor, England. The Order of the Garter is the senior and oldest British Order of Chivalry, founded by Edward III in 1348. Membership in the order is limited to the sovereign, the Prince of Wales, and no more than twenty-four members. (Photo by Gareth Cattermole - WPA Pool/Getty Images) — A general view during the annual Order of the Garter Service at St George's Chapel, Windsor Castle (Gareth Cattermole / WPA Pool/ Getty Images)

Senior Royals assembled at Windsor Castle today - in glorious sunshine - for one of the barmiest and most spectacular pieces of pageantry in existence, the Order of the Garter ceremony, which was founded by Edward III in 1348, and, some say, celebrates his mistress's underwear.

WINDSOR, ENGLAND - JUNE 18: Queen Elizabeth II, Prince Philip, Duke of Edinburgh and other members of the Royal Family walk from Windsor Castle to King George VI chapel for the Order of the Garter ceremony on June 18, 2011 in Windsor, England. The Order of the Garter is the senior and oldest British Order of Chivalry, founded by Edward III in 1348. Membership in the order is limited to the sovereign, the Prince of Wales, and no more than twenty-four members. (Photo by Steve Parsons - WPA Pool/Getty Images) — Queen Elizabeth II, Prince Philip, Duke of Edinburgh and other members of the Royal Family walk from Windsor Castle to King George VI chapel for the Order of the Garter ceremony (WPA Pool / Getty Images)

WINDSOR, ENGLAND - JUNE 18: (L-R) Sophie Rhys-Jones, Countess of Wessex, Catherine, Duchess of Cambridge and Camilla, Duchess of Cornwall attend the annual Order of the Garter Service at St George's Chapel, Windsor Castle on June 18, 2011 in Windsor, England. The Order of the Garter is the senior and oldest British Order of Chivalry, founded by Edward III in 1348. Membership in the order is limited to the sovereign, the Prince of Wales, and no more than twenty-four members. (Photo by Paul Edwards - WPA Pool/Getty Images) — Sophie Rhys-Jones, Countess of Wessex, Catherine, Duchess of Cambridge and Camilla, Duchess of Cornwall attend the annual Order of the Garter Service at St George's Chapel (WPA Pool / Getty Images)

Membership of the order is the highest honour the Queen can bestow, and is limited to just 24 members, who have to wear very silly hats indeed, as these pictures show.

WINDSOR, ENGLAND - JUNE 18: Catherine, Duchess of Cambridge watches her husband Prince William, Duke of Cambridge at the annual Order of the Garter Service at St George's Chapel, Windsor Castle on June 18, 2011 in Windsor, England. The Order of the Garter is the senior and oldest British Order of Chivalry, founded by Edward III in 1348. Membership in the order is limited to the sovereign, the Prince of Wales, and no more than twenty-four members. (Photo by Paul Edwards - WPA Pool/Getty Images) — Prince William today. Membership in the order is limited to the sovereign, the Prince of Wales, and no more than twenty-four members (WPA Pool / Getty Images)

William is one of the newest members of the Order.

WINDSOR, ENGLAND - JUNE 18: Queen Elizabeth II and Prince Philip, Duke of Edinburgh attend the annual Order of the Garter Service at St George's Chapel, Windsor Castle on June 18, 2011 in Windsor, England. The Order of the Garter is the senior and oldest British Order of Chivalry, founded by Edward III in 1348. Membership in the order is limited to the sovereign, the Prince of Wales, and no more than twenty-four members. (Photo by Gareth Cattermole - WPA Pool/Getty Images) — Queen Elizabeth II and Prince Philip, Duke of Edinburgh (Gareth Cattermole / WPA Pool/ Getty Images)