KAZIRANGA, ASSAM - APRIL 13: Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge smile as they visit the Elephant Family Discovery centre, a Mark Shand Foundation charity in Kaziranga National Park on day 4 of the royal visit to India and Bhutan on April 13, 2016 in Kaziranga, India. The Duke and Duchess of Cambridge are on a week-long tour of India and Bhutan taking in Mumbai, Delhi, Assam, Bhutan and Agra. (Photo by Chris Jackson/Getty Images)

KAZIRANGA, ASSAM - APRIL 13:  Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge smile as they visit the Elephant Family Discovery centre, a Mark Shand Foundation charity in Kaziranga National Park on day 4  of the royal visit to India and Bhutan on April 13, 2016 in Kaziranga, India. The Duke and Duchess of Cambridge are on a week-long tour of India and Bhutan taking in Mumbai, Delhi, Assam, Bhutan and Agra.  (Photo by Chris Jackson/Getty Images)