Kate Middleton Joined Three Queens for One of the Fanciest Occasions of the Year

Kate Middleton started off the week on a very fancy note as she stepped out with the royal family for Garter Day, one of the most formal events on the Queen's calendar.

On Monday, she joined Queen Elizabeth, Prince William, Prince Charles, and Camilla Parker-Bowles for the annual Order of the Garter event, during which the Queen and the Knights process in grand ceremonial dress, including velvet robes and plumed hats.

The event celebrates the Order of the Garter, one of the oldest and most senior order of knighthood in the U.K. In 2008, Prince William was made a Knight in the most senior order of chivalry in the U.K.

For the royal occasion, the Duchess of Cambridge wore a white Catherine Walker coatdress with black suede Prada cutout pumps, along with Princess Diana's Collingwood pearl earrings, which she first wore in 2017 for a Spanish state banquet. Ever the queen of re-wearing, Kate also topped off her look with her beloved Lock & Co. fascinator.

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Along with members of the British royal family (including Sophie, Countess of Wessex), Queen Máxima of the Netherlands and Queen Letizia of Spain were also in attendance. Following the event, Kate and William departed with the King and Queen of Spain in a carriage.

Absent from the event were Prince Harry and Meghan Markle — royal expert Marlene Koenig told Harper's Bazaar in 2018 that since Prince Harry is not yet a Knight of the Order of the Garter, he "will probably not be invested until his father is King."

"The Duchess of Sussex has never attended and will probably not attend until Harry is named," Koenig added.