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FILE - In this file photo dated Monday, July 4, 2011, Britain's Prince William, the Duke of Cambridge, is seen at the controls of a helicopter in Dalvay-by-the-Sea on Prince Edward Island, during the Royal Tour of Canada. Britain’s second-in-line to the throne has shared his experiences in a BBC TV documentary broadcast Tuesday Sept. 20, 2016, revealing details about ‘dark moments’ in his job as an air ambulance pilot even as he spoke of the strength he takes from the camaraderie of being part of a four-person helicopter crew. (AP Photo/Robert F. Bukaty, FILE)

FILE - In this file photo dated Monday, July 4, 2011, Britain's Prince William, the Duke of Cambridge, is seen at the controls of a helicopter in Dalvay-by-the-Sea on Prince Edward Island, during the Royal Tour of Canada. Britain’s second-in-line to the throne has shared his experiences in a BBC TV documentary broadcast Tuesday Sept. 20, 2016, revealing details about ‘dark moments’ in his job as an air ambulance pilot even as he spoke of the strength he takes from the camaraderie of being part of a four-person helicopter crew. (AP Photo/Robert F. Bukaty, FILE)

Royals William and Kate in Singapore

Britain's Prince William and his wife Catherine arrive in Singapore Tuesday, kicking off a nine-day Southeast Asian and Pacific tour marking Queen

Elizabeth II's Diamond Jubilee.