St. James's Palace has confirmed that Prince William and Kate Middleton are expecting their first child.
"Their Royal Highnesses the Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby," the palace revealed in a statement.
"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."
Middleton was admitted to King Edward VII Hospital in London with hyperemesis gravidarum, a severe form of morning sickness that requires supplementary hydration and nutrients.
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"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."
According to the Daily Mirror, the royal couple became aware of the pregnancy only "recently," said a royal spokesman. It's likely that Kate's pregnancy has not passed the 12-week point.
Reuters reports that British Prime Minister David Cameron has offered his congratulations to the couple.
"I'm delighted by the news that the Duke and Duchess of Cambridge are expecting a baby," Cameron posted on Twitter. "They will make wonderful parents."
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William is second in line to the throne after his father, Prince Charles. William and Kate's first child stands an excellent chance of becoming monarch one day.
Last year Britain changed the rules of royal succession so that sons no longer have precedence as heir, regardless of age.
Will and Kate currently reside in north Wales where the prince is based as a Royal Air Force search and rescue pilot.