Prince William Joins King Charles and Queen Camilla for Historic Ceremony — in Ostrich Feather Hats!

The Prince of Wales was watched by his wife, Kate Middleton, as he took part in the annual Order of the Garter parade at Windsor Castle

Prince William is taking part in an annual royal tradition for the first time as heir to the throne.

Watched by his wife, Kate Middleton, and resplendent in a hat complete with white ostrich and black heron feathers as well as a dark blue velvet robe, the Prince of Wales — who celebrates his 41st birthday on Wednesday — marched in the annual Order of the Garter procession at Windsor Castle on Monday.

There's a reason Prince William's robe, or mantle, looks familiar — he recently wore the Order of the Garter vestment at his father King Charles' coronation in May.

Garter Day takes place every June with a grand procession of the knights at Windsor Castle accompanied by a marching band and Officers of the Order. The day begins with the monarch formally investing any new Companions with the Order's insignia in the Throne Room of Windsor Castle — this year, those new members are Baroness Ashton of Upholland GCMG and the Lord Patten of Barnes CH. The members and officers attend a lunch hosted by the sovereign, and then all process on foot to a service in St. George's Chapel for a short service where new Companions are installed.

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Following King Charles, who was leading the family in the walk for the first time as monarch, William and other royals processed to St. George’s Chapel watched by hundreds of well-wishers gathered on the castle's lawns.

Among those in the procession, for her first time as Queen, was Camilla, 75. Other prominent knights, like the former U.K. prime ministers, made up the rest.

Following the service, the royals take a horse-drawn carriage ride back up to Windsor Castle.

Notably absent from the outing was Prince Andrew. Even though King Charles' brother is a member of the order, he has been barred from taking a public role for the last two years. However, Prince Andrew – who was disgraced after his disastrous interview in which he tried to justify his friendship with convicted sex offender Jeffrey Epstein — is thought to be joining the lunch and reception at the castle after the service.

Prince Andrew, 63, was allowed to wear his elaborate Order of the Garter robes to the coronation of his brother Charles.

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The Most Noble Order of the Garter, which was established by King Edward III nearly 700 years ago, is the oldest British order of chivalry and the world’s oldest national order of knighthood.

Membership of the order is limited to the monarch, the Prince of Wales, royals both from the U.K. and abroad and 24 Companions, and appointments are at the monarch's sole discretion to recognize public service or personal service to the sovereign. The knights, now both male and female, used to be limited to aristocracy, but today they are chosen from a variety of backgrounds.

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King Charles was appointed to the Order in 1958, while Prince William received his Order of the Garter knighthood in 2008 — and his then-girlfriend Kate attended his first service as a member!

Princess Kate's outfit for Monday's event was reminiscent of her debut at the event 15 years ago — for both outings, she wore black and white polka dot ensembles. Back in 2008, she opted for a black coat dress with tiny white dots, and for her Princess of Wales debut at the event, she chose a white dress with black spots.

Other members of the royal family who are Companions in the Order include Princess Anne, Prince Edward, the Duke of Kent, the Duke of Gloucester and Princess Alexandra.

King Felipe of Spain and King Willem-Alexander of the Netherlands were both installed as members of the Order at the Garter Day in 2019. Several other foreign monarchs are also companions, including Queen Margrethe of Denmark, King Carl Gustaf of Sweden and King Harald of Norway.

Prince Edward and Sophie, the Duke and Duchess of Edinburgh both attended Monday's outing, which fell on a special milestone: their 24th wedding anniversary.

The event came during a busy public period for the family. Over the weekend, Princess Kate and Prince William celebrated Father’s Day with their three children — Prince George, 9, Princess Charlotte, 8, and Prince Louis, 5 — after the annual Trooping the Colour parade on Saturday. This week also sees the Royal Ascot horse race meeting, which most royal family members are expected to attend.

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