Britain's Catherine, Duchess of Cambridge, arrives at a gala dinner in aid of Action on Addiction hosted by the 100 Women in Hedge Funds Philanthropic Initiatives in London October 24, 2013. REUTERS/Ian West/Pool (BRITAIN - Tags: ROYALS ENTERTAINMENT) 

Britain's Catherine, Duchess of Cambridge, arrives at a gala dinner in aid of Action on Addiction hosted by the 100 Women in Hedge Funds Philanthropic Initiatives in London October 24, 2013. REUTERS/Ian West/Pool (BRITAIN - Tags: ROYALS ENTERTAINMENT) 

Britain's Prince William and his wife Catherine, Duchess of Cambridge appear with their baby son, outside the Lindo Wing of St Mary's Hospital, in central London July 23, 2013. Kate gave birth to the couple's first child, who is third in line to the British throne, on Monday afternoon, ending weeks of feverish anticipation about the arrival of the royal baby. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SOCIETY ROYALS ENTERTAINMENT HEALTH) 

Britain's Prince William (L) and Catherine, Duchess of Cambridge arrive at Westminster Abbey to celebrate the 60th anniversary of Queen Elizabeth's coronation in London June 4, 2013. Britain's Queen Elizabeth II returns to the scene of her coronation on Tuesday to mark a reign that has weathered six decades of social transformation and the end of her country's global empire. REUTERS/Andrew Winning (BRITAIN - Tags: ROYALS ENTERTAINMENT)

Britain's Prince William (unseen) and Catherine, the Duchess of Cambridge, visit the Kranji Commonwealth War Cemetery in Singapore September 13, 2012. The royal couple are at their first stop of a nine-day tour of Southeast Asia and the South Pacific on behalf of Queen Elizabeth II to commemorate her Diamond Jubilee. REUTERS/Nicolas Asfouri/Pool (SINGAPORE - Tags: ROYALS ENTERTAINMENT POLITICS) 

Britain's Prince William (unseen) and Catherine, the Duchess of Cambridge, visit the Kranji Commonwealth War Cemetery in Singapore September 13, 2012. The royal couple are at their first stop of a nine-day tour of Southeast Asia and the South Pacific on behalf of Queen Elizabeth II to commemorate her Diamond Jubilee. REUTERS/Nicolas Asfouri/Pool (SINGAPORE - Tags: ROYALS ENTERTAINMENT) 

Britain's Catherine, the Duchess of Cambridge, smiles during a ceremony naming an orchid hybrid in honour of her and Prince William at the National Orchid Garden in the Singapore Botanic Gardens September 11, 2012. The garden is the first stop for the royal couple, who is on their three-day tour of the city-state as part of a tour to mark Queen Elizabeth II's Diamond Jubilee. The orchid hybrid named in their honour is called the Vanda William Catherine. REUTERS/Stephen Morrison/Pool (SINGAPORE - Tags: ENTERTAINMENT ROYALS POLITICS TRAVEL) 

Britain's Catherine, Duchess of Cambridge, looks at the crowds as she arrives with Prince William at Raffles Hotel in Singapore September 11, 2012. The royal couple is in the city-state for a three-day visit starting on Tuesday as part of a tour to mark Queen Elizabeth II's Diamond Jubilee. REUTERS/Tim Chong (SINGAPORE - Tags: ROYALS TRAVEL POLITICS ENTERTAINMENT) 

Britain's Catherine, Duchess of Cambridge arrives for the 'Our Greatest Team Rises' event to celebrate TeamGB and ParalympicsGB at the Royal Albert Hall, in central London May 11, 2012. REUTERS/Alastair Grant/Pool (BRITAIN - Tags: ENTERTAINMENT SOCIETY SPORT OLYMPICS ROYALS) 

Britain's Catherine, Duchess of Cambridge arrives for the 'Our Greatest Team Rises' event to celebrate TeamGB and ParalympicsGB at the Royal Albert Hall, in central London May 11, 2012. REUTERS/Alastair Grant/Pool (BRITAIN - Tags: ENTERTAINMENT SOCIETY SPORT OLYMPICS ROYALS) 

Britain's Catherine, Duchess of Cambridge, smiles as she arrives at the 10th annual Absolute Return for Kids (ARK) gala dinner at Kensington Palace in London June 9, 2011. REUTERS/Arthur Edwards/Pool (BRITAIN - Tags: ROYALS) 

Britain's Catherine, Duchess of Cambridge, arrives at the 10th annual Absolute Return for Kids (ARK) gala dinner at Kensington Palace in London June 9, 2011. REUTERS/Arthur Edwards/Pool (BRITAIN - Tags: ROYALS) 

Catherine, Duchess of Cambridge, and wife of Britain's Prince William, leaves after visiting the University of Calgary hospital during their trip to Calgary, Alberta, July 7, 2011. The Prince and his wife are on a royal tour of Canada from June 30 to July 8. REUTERS/Todd Korol (CANADA - Tags: ROYALS ENTERTAINMENT POLITICS) 

Catherine, Duchess of Cambridge, and wife of Britain's Prince William arrives in Calgary, Alberta July 7, 2011. The Prince and his wife are on a royal tour of Canada from June 30 to July 8. REUTERS/Phil Noble (CANADA - Tags: ROYALS POLITICS ENTERTAINMENT) 

Britain's Catherine, Duchess of Cambridge, arrives at the Santa Barbara Polo and Racquet Club for a charity event held in support of the American Friends of The Foundation of Prince William and Prince Harry in Santa Barbara, California July 9, 2011. REUTERS/Alex Gallardo (UNITED STATES - Tags: ROYALS SOCIETY ENTERTAINMENT) 

Catherine, Duchess of Cambridge, arrives with her husband Britain's Prince William at the Santa Barbara Polo and Racquet Club for a charity event held in support of the American Friends of The Foundation of Prince William and Prince Harry in Santa Barbara, California July 9, 2011. REUTERS/Phil Noble (UNITED STATES - Tags: ROYALS SOCIETY ENTERTAINMENT) 

Britain's Prince William and Catherine, Duchess of Cambridge, arrive at a reception in aid of the National Memorial Arboretum Appeal at St James's Palace, London, November 10, 2011. REUTERS/Lefteris Pitarakis/Pool (BRITAIN - Tags: ENTERTAINMENT ROYALS) 

Britain's Catherine, Duchess of Cambridge, talks to guests at a reception in aid of the National Memorial Arboretum Appeal at St James's Palace, London, November 10, 2011. REUTERS/Lefteris Pitarakis/Pool (BRITAIN - Tags: ENTERTAINMENT ROYALS)