BRISBANE, AUSTRALIA - APRIL 19:  Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge bow their heads in prayer after planting a tree at the Memorial Garden during a visit to the Royal Australian Airforce Base at Amberley on April 19, 2014 in Brisbane, Australia. The Duke and Duchess of Cambridge are on a three-week tour of Australia and New Zealand, the first official trip overseas with their son, Prince George of Cambridge. (Photo by Dan Peled - Pool/Getty Images)