Published Monday, 03 December 2012
News of the royal baby comes after months of speculation about when such an announcement could be expected.
Kate has been admitted to a central London hospital with acute morning sickness and is expected to remain there for several days.
"The Duchess was admitted this afternoon to King Edward VII Hospital in central London with hyperemesis gravidarum," a statement from the palace explained.
"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."
Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting a baby.
St James’s Palace
It is understood that the pregnancy is not yet passed the 12-week stage, but the palace made the announcement due to Kate's condition.
St James's Palace also confirmed that William is by his wife's side in hospital, but it is not clear whether he made the journey there with her.
Kate appeared well at her last public engagement on Friday, so it is thought that her condition developed over the weekend. She was driven to hospital by car, rather than taken in an ambulance.
Hyperemesis gravidarum is considered rare and is thought to affect as few as 0.3% and probably no more than 2% of pregnant women.
Lasting past the first three months and sometimes beyond 21 weeks, symptoms include severe nausea and vomiting - even of blood - and also low blood pressure, an accelerated heart rate, headaches, lethargy and confusion.
It can cause malnutrition, dehydration and other serious complications in sufferers.
However, both families - including the Queen and Duke of Edinburgh, Prince Charles and Camilla, and Prince Harry - are said to be delighted with the news of the pregnancy.
While William and Kate have been keen to start a family, the baby will also have huge significance for the future of the monarchy - as a future king or queen who will be born third in line to the throne.
When William was born, in June 1982, thousands of people gathered outside Buckingham Palace to wait for the birth to be formally announced.
Speculation is already rife as to potential names for the new royal baby.
The news has been welcomed by the Archbishop of Canterbury, who married the royal couple in Westminster Abbey in April last year.
"The whole nation will want to join in celebrating this wonderful news," Rowan Williams said.
"We wish the Duchess the best of health and happiness in the months ahead."
© UTV News