The occasion was the annual Order of the Garter ceremony, where Prince William – smiling himself, somewhat bashfully, before turning to chat with his father, Prince Charles, at his side – marched down the hill from Windsor Castle.
Wearing a dove gray long coat and matching fascinator, the Duchess arrived in a burgundy Rolls-Royce and then, with Camilla, greeted some family friends and walked under a canopy over the chapel's Galilee Porch, only to slip out of public view.
It took Camilla's guiding hand to bring her back before the appreciative crowd – which cheered and applauded. The two women even posed for a camera-bearing female member of the entourage.
"She was a little bit nervous to start with," observed Sandy Fullicks, from Surrey, "but she was quite comfortable. She fits in beautifully."
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William was made a Knight of the Garter, becoming the 1,000th member of the Order – founded more than 600 years ago by Edward III, who sought to institute a band of knights similar to those on King Arthur's Round Table. Membership is restricted to Royals and 24 others, such as former prime ministers.