St. James's Palace said Monday that the Duchess of Cambridge - formerly known as Kate Middleton - has a severe form of morning sickness and is currently in a London hospital.
The palace said that since the pregnancy is in its "very early stages," the 30-year-old duchess is expected to stay in the hospital for several days and will require a period of rest afterward.
In recent days, Middleton has kept up royal appearances - recently playing field hockey with schoolchildren at her former school.
The confirmation of her pregnancy - following intense speculation ever since their lavish Westminster Abbey wedding last year - was greeted with congratulations.
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Prime Minister David Cameron wrote on Twitter that he was "delighted by the news," saying the royals "will make wonderful parents."
Not only are the attractive young couple popular - with William's easy common touch reminding many of his mother, the late Princess Diana - but their child is expected to play an important role in British national life for decades to come.
As the first-born to William - who is second in line for the throne after his father, Prince Charles - the couple's child stands an excellent chance of one day becoming monarch.
Whether boy or girl, the child will be next in line behind William in the line of succession to the throne, Cabinet Office officials have said.
Leaders of Britain and the 15 former colonies that have the monarch as their head of state agreed in 2011 to new rules which give females equal status with males in the order of succession.
Although none of the nations had legislated to make the change as of September 2012, the British Cabinet Office confirmed that this is now the de-facto rule.