Princess Elizabeth with her husband Prince Philip Duke of Edinburgh and their children Prince Charles and Princess Anne. (Photo by Keystone/Getty Images). August 1951

Zoo keeper Ross Poulter holds a White's Tree Frog in Edinburgh Zoo's new tropical forest zone on September 9, 2011 in Edinburgh, Scotland. The Brilliant Birds Exhibit which brings together beautiful and rare birds from all over the world is now more colourful and unusual, with the unveiling of the zoo's new tropical forest zone bringing together a collection of vertebrates, invertebrates and amphibians for the very first time. (Photo by Jeff J Mitchell/Getty Images)

The Royal Air Force aerobatic team, the Red Arrows, perform during The Royal International Air Tattoo at the RAF in Fairford July 11, 2014. (Photo by Stefan Wermuth/Reuters)

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge walk hand in hand from Buckingham Palace the day after their wedding to a waiting helicopter as they leave for a secret honeymoon location, on April 30, 2011 in London, England. The marriage of Prince William and Catherine Middleton was led by the Archbishop of Canterbury and was attended by 1900 guests, including foreign Royal family members and heads of state. Thousands of well-wishers from around the world have also flocked to London to witness the spectacle and pageantry of the Royal Wedding. (Photo by John Stillwell - WPA Pool/Getty Images)

Britain's Prince Harry meets Chewbacca during a visit to the Star Wars film set at Pinewood Studios near Iver Heath, west of London, Britain, April 19, 2016. Prince William and Prince Harry are touring Pinewood to visit the production workshops and meet the creative teams working behind the scenes on the Star Wars films. (Photo by Adrian Dennis/Reuters)

Dr. Hannah Cobb from The University of Manchester looks at a viking sword during a viewing at CFA Archaeology of artefacts discovered from the first fully intact Viking boat burial site on October 18, 2011 in Edinburgh, Scotland. (Photo by Jeff J Mitchell/Getty Images)

Princess Anne, Princess Royal waves off Zara Philips as she eaves Canongate Kirk on the afternoon of her wedding to Mike Tindall on July 30, 2011 in Edinburgh, Scotland. (Photo by Chris Jackson PT/Getty Images)

Corporal of Horse Andy Radford prepares to mount his horse in the parade square at Hyde Park Barracks on April 15, 2011 in London, England. Members of the Household Cavalry gave a behind the scenes tour of many of the duties performed as part of their daily routine, including special preparation ahead of the forthcoming Royal Wedding. The Household Cavalry will perform several ceremonial duties during the summer, including the Royal Wedding on April 29, and the Queen's Birthday Parade (Trooping the Colour) in June. (Photo by Dan Kitwood/Getty Images)