The Duke and Duchess of Cambridge are expecting a baby, St James’ Palace announced today.
A spokesman said the Queen and Duke of Edinburgh, the Prince of Wales and members of both families are delighted with the news, with David Cameron tweeting: “they will make wonderful parents”.
The palace said the duchess was admitted this afternoon to the King Edward VII Hospital in central London with acute morning sickness, known as hyperemesis gravidarum, and is expected to stay in hospital for several days.
A spokesman said: “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.”
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 their vomiting can be so severe 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 confirmed that William is by his wife's side in hospital but would not comment on whether he travelled with her to hospital.
Kate made the journey from Bucklebury in Berkshire, where her parents Michael and Carole Middleton live, and it is thought she spent the weekend with them.
The Duke and Duchess of Cambridge's baby will be born third in line to the throne and a great grandchild to the Queen.
Thanks to the proposed radical shake up of the monarchy's rules of succession, the sex of the royal infant will not determine whether he or she wears the crown.
This baby will be a future king or queen regardless.
In October 2011, David Cameron announced that the 16 Commonwealth countries where the Queen is head of state had agreed to give female royals the same rights of succession as their brothers.
Under the ancient rules of male primogeniture, first born royal daughters in direct line to the throne were leapfrogged by their younger male siblings.
The last time a still-serving monarch got to meet a great grandchild born in direct succession to the crown was nearly 120 years ago.
Queen Victoria, who reigned until 1901, was still sovereign when her great grandchild Edward VIII, who later abdicated, was born third in line in 1894.
His brother George VI was also born in Queen Victoria's lifetime, arriving fourth in line in 1895.
The last great granddaughter of a still-serving sovereign born in direct succession on the male line was their sister Princess Mary in 1897.
William and Kate's baby will be the great great great great great grandchild of Queen Victoria.
When the newest addition to the Royal Family arrives, Prince Harry, the baby's uncle, will be bumped down the line of succession to fourth place.
What do you think Wills and Kate should name their baby? Vote here