THIMPHU, BHUTAN - APRIL 15:  Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge trek up to Tiger's Nest during a visit to Bhutan on the 15th April 2016 in Thimphu, Bhutan. The Royal couple are visiting Bhutan as part of a week long visit to India and Bhutan that has taken in cities such as Mumbai, Delhi, Kaziranga, Bhutan and Agra.  (Photo by Mark Large - Pool/Getty Images)