The Duke and Duchess of Cambridge are expecting a baby, St James's Palace has announced.
Months of speculation about a royal pregnancy were ended on Monday afternoon when William and Kate told the world they will be parents for the first time.
But the announcement also revealed the Duchess is being treated for very acute morning sickness - hyperemesis gravidarum - at a private London hospital.
The Duke was by her side after she was admitted to the King Edward VII Hospital, where she is expected to remain for a few days.
The Queen and Duke of Edinburgh, the Prince of Wales and members of both families are delighted with the news, said a St James's Palace spokesman.
Babies were the topic of conversation when William and Kate visited Cambridge last week for the first time as a married couple. The Duke, an RAF search and rescue pilot, was given a tiny baby romper suit made by well-wisher Samantha Hill, 27, from Sudbury, Suffolk, which was decorated with a picture of a helicopter and the words "Daddy's little co-pilot".
The baby theme continued when Kate met Tessa Davies, 35, from Cambridge, who had given her son five-month-old James the middle name William in honour of the Duke and had brought him to meet the royal couple.
St James's Palace would not say when the royal couple became aware of the pregnancy, only saying "recently".
It is understood that the pregnancy has not passed the 12-week point and today's announcement was prompted by the Duchess's medical condition. For women with hyperemesis gravidarum, vomiting can be so severe that they cannot keep food or liquid down. The condition usually continues past the first three months of pregnancy and can pass by week 21, but may also last longer.
St James's Palace said in 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. The Duchess was admitted this afternoon to King Edward VII Hospital in central London with hyperemesis gravidarum. 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."