Kate Middleton Returns to Royal Event Where She's Supported Prince William Since Before Their Marriage

The Princess of Wales stepped out at the Order of the Garter ceremony, where she made her debut in 2008 — three years before her royal wedding

Kate Middleton is all smiles as Prince William takes part in one of the oldest royal traditions: the Order of the Garter service.

The Princess of Wales, 41, supported her husband on Monday as he made his debut as the Prince of Wales at the Order of the Garter ceremony and procession at Windsor Castle. Kate watched as Prince William, King Charles, Queen Camilla and other members of the royal family donned ornate blue robes and hats featuring an ostrich plume at the prestigious event dating back centuries.

Princess Kate exchanged a grin with Prince William as he processed past her. And when King Charles and Queen Camilla walked by, she dipped into a curtsy.

According to the royal family's website, King Edward III (who ruled from 1327 to 1377) was so inspired by tales of King Arthur and the Knights of the Round Table that he set up his own group of honorable knights called the Order of the Garter.

RELATED: How Kate Middleton's Trooping the Colour Outfit Was the Ultimate Supportive Wife Move

In addition to the ceremony having historic roots, it is also a milestone in Prince William and Princess Kate's relationship. Kate made her debut at the event in 2008 as William's girlfriend when he received his Order of the Garter knighthood. Wearing an elegant black and white outfit, Kate was spotted chatting with Prince Harry and Camilla.

Kate's attendance was significant, showing that she was being welcomed into the royal family fold.

The now-Prince and Princess of Wales met as students at the University of St. Andrews in Scotland. Three years after Kate's outing at the Order of the Garter service, the pair married at Westminster Abbey.

Over the past 15 years, Kate has attended the Order of the Garter ceremony with the royal family on many occasions.

For this year's service, the Princess of Wales wore a long-sleeved white dress with black polka dots by Alessandra Rich paired with a coordinating hat by Philip Treacy. The look was strikingly similarly to her 2008 look at the debut, when she wore a black ensemble with white dots. Her hair was swept into an elegant updo.

Kate accessorized with the Collingwood pearl and diamond earrings that previously belonged to her late mother-in-law, Princess Diana. The jewels were a key part of Diana's jewelry box, and Princess Kate has worn them on numerous occasions — sometimes pairing them with a tiara for glamorous palace events.

At several points, Kate and those participating in the procession held onto their hats due to wind gusts.

She stood with Sophie, the Duchess of Edinburgh, who sported a sleeveless dress by Emilia Wickstead decorated in a pink and green floral pattern topped with a  Jane Taylor hat.

The event coincided with a special day for Prince Edward and Sophie: their 24th wedding anniversary!

The Most Noble Order of the Garter 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 from the U.K. and abroad and just 24 Companions, and appointments are at the monarch's sole discretion to recognize public service or personal service to the sovereign.

Several members of the British royal family are members including Queen Camilla, Princess Anne, Prince Edward, the Duke of Kent, the Duke of Gloucester and Princess Alexandra. Royals from around the world — such as King Felipe of Spain, King Willem-Alexander of the Netherlands, Queen Margrethe of Denmark, King Carl Gustaf of Sweden and King Harald of Norway — also hold the position.

Prince William and other Companions wore the Order of the Garter robe, or mantle, last month at King Charles and Queen Camilla's coronation. For the crowning ceremony, Kate wore the mantle of the Royal Victorian Order. Queen Elizabeth named her granddaughter-in-law a Dame Grand Cross of the Royal Victorian Order in April 2019, coinciding with Kate and William's eighth wedding anniversary.

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Over the weekend, the royal family marked the first Trooping the Colour of King Charles' reign. The annual event is the public celebration of the British monarch's birthday, marked by a grand procession through London and a Buckingham Palace balcony gathering. Prince William and Princess Kate were joined by their three children — Prince George, 9, Princess Charlotte, 8, and Prince Louis, 5 — at the event.

The family also released two new portraits to celebrate Father's Day. In the snaps, taken earlier this year at Windsor, Prince William is surrounded by his three children.

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