The Duke And Duchess Of Cambridge Visit The National September 11 Memorial Museum [Getty Images]

NEW YORK, NY - DECEMBER 09: Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge visit the National September 11 Memorial & Museum on December 09, 2014 in New York City. The couple, who are traveling without their son Prince George, are on a three-day US east coast visit. This is the Duke and Duchess' first official visit to New York City. ( Photo By Robert Sabo - Pool/Getty Images)

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