In a dedication to the U.K.'s dead servicemen and women, William laid a wreath at the leading London war memorial, the Cenotaph in Whitehall.
Kate, meanwhile, stood in a window of the nearby Foreign and Commonwealth Office and watched William, 29, in his gray Royal Air Force uniform. Alongside her: Camilla, Duchess of Cornwall and Sophie, Countess of Wessex. The Duchess of Cambridge wore two poppies, Britain's traditional symbol of remembrance, pinned to her black coat – and she stood with her head slightly bowed during the two minutes of silence.
William, who has lost friends in combat in Iraq and Afghanistan, stood solemn-faced alongside the ranks of soldiers, sailors and pilots who attended the memorial, which took place just a few hundred yards from Westminster Abbey, where William and Kate wed in April.
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William offered a white-gloved salute after his tribute.
Observers said that Camilla, 64, seemed to be giving Kate some words of advice during the 22-minute service, which also included a brief set of prayers and hymns. "She was chatting quite a lot [with] Camilla, who seemed to be telling her what was going on," says one.
Prince Harry, who is currently in the United States, is expected to pay his respects at the Gila Bend base in Arizona, where he's currently training.