Duchess Kate observes Remembrance Sunday on Nov. 13. Credit: Justin Tallis/AFP/Getty Images

Prince William and Duchess Kate honored the members of their nation's armed forces who died in the line of duty during a Remembrance Day ceremony in London on Sunday, November 13.

The couple joined Queen Elizabeth II, Prince Philip, Prince Charles, Prince Harry, Duchess Camilla, Countess Sophie and more members of the royal family as they observed the memorial day at the Cenotaph war memorial on Whitehall.

The Duchess of Cambridge, 34, looked elegant in a Lio coat and a black lace dress, both designed by Diane von Furstenberg, as she watched the service from a balcony in the Foreign Office. She paired the chic look with a black John Boyd hat and diamond and pearl earrings borrowed from the queen. On her jacket, Kate wore three red poppies in honor of the fallen World War I soldiers and veterans.

Also dressed in black, Queen Elizabeth II, 90, laid a wreath made of poppies at Sir Edwin Lutyens' war memorial as thousands watched from Whitehall. Prince Philip, Prince Charles, Prince William and Prince Harry were among the other royals who also laid wreaths. 

Prince William, 34, and Prince Harry, 32, both wore military uniforms as they stood at attention.

This year's ceremony marks the centenaries of the Battle of the Somme and the Battle of Jutland, the 25th anniversary of the Gulf War and the 80th anniversary of the first flight of the Supermarine Spitfire.

A day earlier, the royals remembered the fallen at the annual Royal Festival of Remembrance at London's Royal Albert Hall.

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