Britain's Prince William and Kate, the Duchess of Cambridge, with son Prince George, stand atop of the stairs and wave good bye as they board their flight in Canberra, Australia.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge attend a reception hosted by the Governor General Peter Cosgrove and Her excellency Lady Cosgrove at Government House, April 24, 2014 in Canberra, Australia.

Prince William, Duke of Cambridge looks on as Catherine, Duchess of Cambridge is shown how to play on DJ decks at the youth community centre, The Northern Sound System in Elizabeth, April 23, 2014, in Adelaide, Australia.

Prince Charles, The Prince Of Wales and Diana, Princess of Wales stand in front of Ayers Rock during their official tour of Australia, March 21, 1983. Right, William and his wife Catherine, Duchess of Cambridge, pose in front of the Uluru, also known as Ayers Rock, April 22, 2014.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge walk down Kuniya Walk at the base of Uluru, April 22, 2014 in Ayers Rock, Australia.

Prince William, Duke of Cambridge, and Catherine, Duchess of Cambridge, meet a Koala at Taronga Zoo on April 20, 2014 in Sydney, Australia.

Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge and Prince George of Cambridge meet a Bilby called George as they visit the Bilby Enclosure at Taronga Zoo on April 20, 2014 in Sydney, Australia.

Prince William, Duke of Cambridge holds Prince George of Cambridge as they look at a Bilby called George at Taronga Zoo on April 20, 2014 in Sydney, Australia.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge arrive at St Andrew's Cathedral for Easter Sunday Service on April 20, 2014 in Sydney, Australia.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge leave St. Andrew's Cathedral following a Easter Sunday Service on April 20, 2014 in Sydney, Australia.

Chief of Air Force Air Marshall Geoff Brown, left, talks with Britain's Prince William sitting in the cockpit of a Super Hornet as his wife Kate, the Duchess of Cambridge, second from right, and Wing Commander Stephen Chappell, right, watch at RAAF Base Amberley, near Brisbane Australia, Saturday April 19, 2014.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge plant a tree as they visits RAAF Amberley on April 19, 2014 in Brisbane, Australia.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge pose with a surfboard they were given as they attend a lifesaving event on Manly Beach on April 18, 2014 in Sydney, Australia.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge arrive at the Winmalee Guide Hall, April 17, 2014 in Winmalee, Australia.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge pose for a photograph at Echo Point with 'The Three Sisters' in the background on April 17, 2014 in Katoomba, Australia.

Prince William, Duke of Cambridge, Prince George of Cambridge and Catherine, Duchess of Cambridge arrive at Sydney Airport on a Australian Airforce 737 aircraft, April 16, 2014 in Sydney.

The Duke and Duchess of Cambridge walk down the stairs of the Sydney Opera House, April 16, 2014 in Sydney.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge are seen lifting the 2015 Cricket World Cup at a 2015 Cricket World Cup event at Latimer Squareon, April 14, 2014 in Christchurch, New Zealand.

Catherine Duchess of Cambridge and Prince William, Duke of Cambridge sample red wine as the visit Otago Wines at Amisfield winery, April 13, 2014 in Queenstown, New Zealand.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge onboard an America's Cup yacht in Auckland Harbour, April 11, 2014 in Auckland, New Zealand.

Catherine, Duchess of Cambridge onboard a Team New Zealand yacht at the Viaduct Basin in Auckland, April 11, 2014, in Auckland, New Zealand.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge meet with Grant Dalton of Team New Zealand on the yacht Imagine at the Viaduct Basin in Auckland, April 11, 2014 in Auckland, New Zealand.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge arrive at Auckland Harbour, April 11, 2014 in Auckland, New Zealand.

Britain's Kate, the Duchess of Cambridge, smiles as she visits the Omaka Heritage Aviation Centre in Blenhiem, New Zealand April 10, 2014.

Britain's Prince William, left, sits in a classic Sopwith Pup as he and his wife Kate, the Duchess of Cambridge, center, tour the Omaka Aviation Heritage Centre in Blenheim, New Zealand April 10, 2014.

Catherine, Duchess of Cambridge watches Prince William, Duke of Cambridge sit in a plane as they attend a WW1 commemorative and Flying Day at Omaka Aviation Heritage Centre April 10, 2014 in Blenheim, New Zealand.

Britain's Prince William speaks with 3-year-old twins Lola and Milly Barnett following a wreath laying ceremony in Blenheim, New Zealand, April 10, 2014.

New Zealand First Lady Bronagh Key, New Zealand Prime Minister John Key and Catherine, Duchess of Cambridge look on as they attend an art unveiling of a portrait of Queen Elizabeth II by New Zealand artist Nick Cuthell at Government House April 10, 2014 in Wellington, New Zealand.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge attend an art unveiling of a portrait of Queen Elizabeth II during Day 4 of a Royal Tour to New Zealand at Government House April 10, 2014 in Wellington, New Zealand.

Britain's Prince George plays with the hair of his mother, Kate, the Duchess of Cambridge, during a visit to Plunket nurse and parents group at Government House in Wellington, New Zealand, April 9, 2014.

Britain's Kate, the Duchess of Cambridge, holds Prince George during a visit to Plunket nurse and parents group at Government House in Wellington, New Zealand, April 9, 2014.

Britain's Prince George, right, plays during a visit to Plunket nurse and parents group at Government House in Wellington, New Zealand, April 9, 2014.

Britain's Prince George plays during a visit to Plunket nurse and parents group at Government House in Wellington, New Zealand, April 9, 2014. Plunket is a national not-for-profit organization that provides care for children and families in New Zealand.

Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge and Prince George of Cambridge arrive at Wellington Airport's military terminal for the start of their tour on April 7, 2014 in Wellington, New Zealand.

Prince William and Catherine Duchess of Cambridge with their son Prince George arrive at Sydney International Airport in Sydney, New South Wales ahead of boarding a Royal New Zealand Air Force aircraft on April 7, 2014 to begin their royal tour of New Zealand and Australia

Britain's Prince William and his wife Kate, the Duchess of Cambridge receive a Maori powhiri at their official welcome ceremony at Government House, in Wellington, New Zealand, April 7, 2014.

Britain's Kate, the Duchess of Cambridge, left, receives a hongi, a traditional Maori welcome, from Maori Elder Hiria Hape, at their official welcome ceremony, in Wellington, New Zealand, April 7, 2014.

Britain's Prince William picks up the dart from a Maori warrior during a Maori welcoming ceremony at Government House in Wellington on April 7, 2014. Britain's Prince William, his wife Kate and their son Prince George are on a three-week tour of New Zealand and Australia.

Britain's Prince William and his wife Catherine meet a Maori warrior during a welcoming ceremony at Government House in Wellington on April 7, 2014. Britain's Prince William, his wife Kate and their son Prince George are on a three-week tour of New Zealand and Australia.

Britain's Prince William reviews the New Zealand Air Force Band at the official welcome ceremony at Government House, in Wellington, April 7, 2014. Prince William and his wife, Kate, arrived in New Zealand's capital to cheers from locals who braved windy, rainy weather to catch a glimpse of the royal couple.