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Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge visit 'Jimmy's', a night shelter, on November 28, 2012 in Cambridge, England. (Photo by Paul Rogers - WPA Pool/Getty Images)

Prince William The Duke of Cambridge (L) and his wife Catherine the Duchess of Cambridge walk together during the opening of the Football Associations National Fooball Centre, St Georges Park in Burton Upon Trent on October 9, 2012. Buckingham Palace announced on December 3, 2012 that Prince William The Duke of Cambridge and his wife Catherine the Duchess of Cambridge are expecting a baby. Adrian Dennis/AFP/Getty Images

Policeman stand guard outside the King Edward VII hospital where the Duchess of Cambridge has been admitted with a severe form of morning sickness, in London, Monday, Dec. 3, 2012. Prince William and his wife Kate are expecting their first child. St. James's Palace announced the pregnancy Monday, saying that the Duchess of Cambridge - formerly known as Kate Middleton - has a severe form of morning sickness and is currently in a London hospital. William is at his wife's side. The palace said since the pregnancy is in its "very early stages," the 30-year-old duchess is expected to stay in the hospital for several days and will require a period of rest afterward. (AP Photo/Alastair Grant)

Britain's Prince William's wife Catherine, the Duchess of Cambridge adjusts her scarf outside a mosque at KLCC in Kuala Lumpur on September 14, 2012, on the second leg of a nine-day Southeast Asian and Pacific tour marking Queen Elizabeth II's Diamond Jubilee. SAEED KHAN/AFP/Getty Images

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge smile as they look at an orchid named in honor of Diana, Princess of Wales at Singapore Botanical Gardens on September 11, 2012 in Singapore. (Photo by Danny Lawson - Getty Images)

Britain's Prince William and his wife Kate, the Duke and Duchess of Cambridge, walk together as they visit the Kranji Commonwealth War Memorial in Singapore on Sept. 13, 2012. Prince William and his wife Catherine are expecting their first child. St. Jamesís Palace announced the pregnancy Monday, saying that the Duchess of Cambridge, formerly known as Kate Middleton has a severe form of morning sickness and is currently in a London hospital. William is at his wife's side. (AP Photo/Nicolas Asfouri)

Kate, the Duchess of Cambridge visits the Kranji Commonwealth War Memorial in Singapore on Sept. 13, 2012. St. James's Palace announced Prince William and his wife Catherine are expecting their first child on Monday, saying that the Duchess of Cambridge, formerly known as Kate Middleton has a severe form of morning sickness and is currently in a London hospital. William is at his wife's side. (AP Photo/Nicolas Asfouri)

Britain's Catherine, Duchess of Cambridge, arrives for an official visit to the CRI Stockton Recovery Service, in Stockton-On-Tees, north-east England on October 10, 2012. Prince William's wife Catherine is expecting a baby, though she is in the hospital suffering severe morning sickness, St James's Palace announced on December 3, 2012. PAUL ELLIS/AFP/Getty Images

Britain's Catherine, Duchess of Cambridge leaves the Natural History Museum in London on November 27, 2012 to officially open the new Treasures Gallery. Treasures is a permanent gallery in the museum's Central Hall and will showcase 22 extraordinary objects from the museum's history, selected for their scientific, cultural and historical worth. ANDREW COWIE/AFP/Getty Images

Britain's Catherine, Duchess of Cambridge, arrives at the Natural History Museum in London on November 27, 2012 to officially open the new Treasures Gallery. Treasures is a permanent gallery in the museum's Central Hall and will showcase 22 extraordinary objects from the museum's history, selected for their scientific, cultural and historical worth. ANDREW COWIE/AFP/Getty Images

Catherine, Duchess of Cambridge talks to Paul Davies (R), a former player and beneficiary of the Charitable Trust which supports injured players in Wales, ahead of the Autumn International rugby match between Wales and New Zealand at the Millennium Stadium, Cardiff on November 24, 2012 in Cardiff, Wales. (Photo by Michael Steele - Getty Images)

Kate, the Duchess of Cambridge, visits the pre-prep school for the under-5s, during her visit to St. Andrew's School, where she attended from 1986 till 1995, in Pangbourne, England, Friday, Nov. 30, 2012. The royal, formerly known as Kate Middleton, played hockey and revealed her childhood nickname - Squeak - when she returned to her elementary school for a visit Friday. Kate told teachers and students at the private St. Andrew's School in southern England that her 10 years there were "some of my happiest years." She said that she enjoyed it so much that she had told her mother she wanted to return as a teacher. (AP Photo/Arthur Edwards)

Kate, the Duchess of Cambridge plays hockey during her visit to St. Andrew's School, where she attended school from 1986 till 1995, in Pangbourne, England, Friday, Nov. 30, 2012. The Duchess of Cambridge has gone back to school. The royal, formerly known as Kate Middleton, played hockey and revealed her childhood nickname - Squeak - when she returned to her elementary school for a visit Friday. Kate told teachers and students at the private St. Andrew's School in southern England that her 10 years there were "some of my happiest years." She said that she enjoyed it so much that she had told her mother she wanted to return as a teacher. (AP Photo/Arthur Edwards)

Kate, the Duchess of Cambridge, centre, plays hockey during her visit to St. Andrew's School, where she attended school from 1986 till 1995, in Pangbourne, England, Friday, Nov. 30, 2012. The Duchess of Cambridge has gone back to school. The royal, formerly known as Kate Middleton, played hockey and revealed her childhood nickname - Squeak - when she returned to her elementary school for a visit Friday. Kate told teachers and students at the private St. Andrew's School in southern England that her 10 years there were "some of my happiest years." She said that she enjoyed it so much that she had told her mother she wanted to return as a teacher. (AP Photo/Arthur Edwards)

Catherine, Duchess of Cambridge visits 'Jimmy's', a night shelter, with Prince William, Duke of Cambridge, on November 28, 2012 in Cambridge, England. (Photo by Paul Rogers - Getty Images)

Kate Britain's Duchess of Cambridge, makes a visit with her husband Prince William to a charity night shelter called Jimmy's in Cambridge England Wednesday Nov. 28, 2012. (AP Photo/ Paul Rogers)

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge receive a painting from former shelter guest Twig during their visit at 'Jimmy's', a night shelter, on November 28, 2012 in Cambridge, England. (Photo by Paul Rogers - Getty Images)

Catherine, Duchess of Cambridge meets Oliver Duell during an official visit to the Guildhall on November 28, 2012 in Cambridge, England. (Photo by Samir Hussein/WireImage)

Britain's Kate, Duchess of Cambridge meets children working on projects as she visits Manor School during an official visit to Cambridge, England on Wednesday Nov. 28, 2012 . (AP Photo/Chris Jackson)

Britain's Prince William, Duke of Cambridge (L) and Britain's Catherine, Duchess of Cambridge (R) speak to dignitaries as they arrive for a visit to Peterborough City Hospital in Peterborough, Cambridgeshire, north of London, on November 28, 2012. Britain's Prince William and his wife Catherine visited the university city that is home to their dukedom on November 28 for the first time since they were given their official titles. LEON NEAL/AFP/Getty Images

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge share a joke as they clap while watching the track cycling on day 1 of the London 2012 Paralympic Games at the Velodrome on August 30, 2012 in London, England. St James's Palace has announced that Prince William and Catherine Duchess Of Cambridge are expecting a baby. (Photo by Chris Jackson/Getty Images)

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge embrace after Philip Hindes, Jason Kenny and Sir Chris Hoy of Great Britain win the gold and a new world record in the Men's Team Sprint Track Cycling final during Day 6 of the London 2012 Olympic Games at Velodrome on August 2, 2012 in London, England. (Photo by Pascal Le Segretain/Getty Images)