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Emma Watson, Daniel Radcliffe and Rupert Grint hit the red carpet in London last night to promote Harry Potter and the Deathly Hallows, Part 1, which opens November 19th. All three adorned their outfits with a poppy pin—Emma affixing hers at the waist of her one-shoulder Vionnet dress—in honor of Remembrance Day, the U.K. and Commonwealth version of Veteran’s Day. While this won’t surprise Canadian, British or Australian readers, Americans who are used to pinning on the American flag may not know the storied history behind the symbol: The red poppy bloomed across Flanders, Belgium, where some of the bloodiest battles of World War I took place. It has since become tradition to wear a red poppy pin today, which marks the official end of the war on November 11th, 1918.