The Duchess of Cambridge has spent the night in hospital with severe morning sickness as the nation celebrates the news that she is pregnant.
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 excitement about the eagerly-anticipated announcement was tinged with concern after it was revealed the Duchess was admitted to a private London hospital for hyperemesis gravidarum - very acute morning sickness.
William was by her side at the King Edward VII Hospital after she was taken there by car from Bucklebury in Berkshire, where her parents Michael and Carole Middleton live. The Duke left the hospital shortly after 8.20pm, while Kate is expected to remain for a few days.
It was reported that the Queen's former gynaecologist Marcus Setchell, who delivered the Countess of Wessex's two children, is treating her. It is understood that the pregnancy has not passed the 12-week point and Monday'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.
But while there is concern for the royal couple, there is excitement across the UK and beyond. Prime Minister David Cameron led the congratulations from the nation when he said: "It's absolutely wonderful news and I'm delighted for them. I'm sure they will make absolutely brilliant parents, and I'm sure everyone around the country will be celebrating with them tonight."
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. A statement read: "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."
Congratulations for the Duke and Duchess poured in from around the world. Julia Gillard, prime minister of Australia, called it "delightful news" and said it would "bring joy to many around the world", while John Key, prime minister of New Zealand, said the nation's women would sympathise with Kate's condition and wished her a speedy recovery.
Jay Carney, press secretary to US president Barack Obama, said: "On behalf of everyone here in the White House, beginning with the President and the First Lady, we extend our congratulations to the Duke and Duchess of Cambridge on the welcome news this morning out of London that they are expecting their first child."