NEW YORK, NY - DECEMBER 09:  Catherine, Duchess of Cambridge, visits the National September 11 Memorial Museum with her husband Prince William, Duke of Cambridge on December 9, 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 Carl Court - WPA Pool/Getty Images)