LONDON - JULY 20:  ()   The Cartier 'Halo' tiara, worn by the Duchess of Cambridge on her wedding day is photographed before it goes on display at Buckingham Palace during the annual summer opening on July 20, 2011 in London, England. The tiara, which was her 'something borrowed', was loaned to the bride by the Queen, a tradition for royal weddings.The Duchess of Cambridge wore the tiara on her wedding day on April 29 to Prince William, Duke of Cambridge. (Photo by Lewis Whyld/WPA Pool/ Getty Images)