Prince William's wife Catherine is expecting a baby and is in hospital with a type of severe morning sickness, the Royal Family has announced.
A spokeswoman for the royal couple said 30-year-old Catherine, widely known as Kate, was in King Edward VII Hospital in central London suffering from hyperemesis gravidarum.
The acute morning sickness causes severe nausea and vomiting and requires supplementary hydration and nutrients.
Prince William, a Royal Air Force helicopter pilot, was at her side and she is likely to remain in hospital for several days, Reuters reports.
There was no detail about when the baby was due, although the prince's spokesman said she was less than 12 weeks pregnant.
In a statement, St James's Palace said: "Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting a baby," adding that the Queen and members of both families were delighted.
The couple, officially known as the Duke and Duchess of Cambridge, married in April last year.
William is second in line to the British throne, and their first child will become the third in succession.
Last year Britain and other Commonwealth countries which have the Queen as their monarch agreed to change the rules of royal succession so that sons would no longer have precedence as heir, regardless of age, Reuters reports.
The agreement also means an end to a ban on a future monarch marrying a Catholic, a stipulation dating back some 300 years.
US President Barack Obama and his wife Michelle were one of the first to send congratulations, an indication of the couple's popularity across the Atlantic.