FILE - In this Friday April 29, 2011 file photo Britain's Prince William and his bride Kate, Duchess of Cambridge, leave Westminster Abbey, London, following their wedding. The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/Tom Hevezi, File)

FILE - In this Wednesday Nov. 28, 2012 file photo Britain's Prince William meets with a young member of the public as she arrives at the Guildhall during a visit to Cambridge England. The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/Arthur Edwards, File)

FILE - In this Wednesday Nov. 28, 2012 file photo Britain's Kate Duchess of Cambridge. left. meets with a young member of the public as she arrives at the Guildhall during a visit to Cambridge England. The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/Arthur Edwards, File)

FILE- Britain's Prince William, left, and his wife Kate, the Duchess of Cambridge, visit a football training pitch at St George's Park near Burton Upon Trent in Staffordshire, England, in this file photo dated Tuesday, Oct. 9, 2012. The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012.(AP Photo/Kirsty Wigglesworth, FILE)

FILE - In this Friday April 29, 2011 file photo Britain's Prince William and his bride Kate, Duchess of Cambridge, leave Westminster Abbey, London, following their wedding. The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/Martin Meissner, File)

FILE - In this June 22, 1982 file photo Britain's Prince Charles, Prince of Wales, with his wife Princess Diana taking their newborn son Prince William, as they left St. Mary's Hospital, Paddington, London. William, the Duke and and Kate, Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/John Redman, File)

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)

FILE - Kate, the Duchess of Cambridge seen during her visit to St. Andrew’s School, where she attended school, in Pangbourne, England, in this file photo dated Friday, Nov. 30, 2012. The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/Arthur Edwards, File)

FILE - In this Friday, Nov. 30, 2012 file photo 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. The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/Arthur Edwards, File)

FILE - In this June 22, 1982 file photo Britain's Prince Charles, Prince of Wales, with his wife Princess Diana taking their newborn son Prince William, as they left St. Mary's Hospital, Paddington, London. William, the Duke and and Kate, Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/John Redman, File)