The Duchess' close pal Jessica Hay went public with the baby news last week (28Nov12), and on Monday (03Dec12) representatives from royal residence St. James Palace revealed the rumours are true.
However, the mum-to-be has been suffering from hyperemesis gravidarum, an acute bout of morning sickness which requires supplementary hydration and nutrients, and is currently being treated by doctors at King Edward VII Hospital.
The statement reads: ""Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting a baby.
""The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall and Prince Harry and members of both families are delighted with the news.
""As the pregnancy is in its very early stages, Her Royal Highness is expected to stay in hospital for several days and will require a period of rest thereafter.""
The Duchess has cancelled her next three official engagements as a result of her hospitalisation.
Prince William, who is second in line to the throne after his father Prince Charles, wed the former Kate Middleton in April, 2011.