Kate Middleton, entered a London hospital on Monday after going into labour, Britain’s royal palace said.
The baby will be the third child for her and husband Prince William and fifth in line to the throne.
The 36-year-old duchess and her husband traveled by car from their Kensington Palace home to the private Lindo Wing of St Mary’s Hospital in central London. The palace said Kate was in “the early stages of labour.”
William and Kate married in 2011 and have two other children: Prince George, 4, and Princess Charlotte, who turns 3 next month. Both were born at the same hospital, as were William and his younger brother Prince Harry.
The baby, whose gender has not been announced, will be Queen Elizabeth II’s sixth great-grandchild and fifth in line to the throne, after grandfather Prince Charles, father Prince William and the two older siblings.
The new arrival will bump Prince Harry to sixth place in the line of succession.
The 36-year-old duchess, formerly Kate Middleton, carried out her last official engagement on March 22 before going on maternity leave.
No exact due date has been given, with officials saying only that the baby was due in April.
As in her previous pregnancies, Kate suffered from hyperemesis gravidarum, a severe form of morning sickness. Officials announced both her previous pregnancies before the traditional 12-week mark because she was too unwell to attend public engagements.
Television crews, journalists and royal fans have set up camp outside the hospital for the “royal baby watch” since early April in anticipation of the arrival.
In a mix of royal tradition and modernity, the birth will be announced with a notice placed on an easel in the forecourt of Buckingham Palace and on royal social media accounts.
Many are betting on a traditional royal name for the baby, with bookmakers saying Mary, Alice, Arthur and James are the most popular guesses. Monday is St George’s Day, England’s national day, but the name is already taken by the baby’s big brother.
Like its older siblings, the baby’s full title will be Her (or His) Royal Highness, Princess (or Prince), followed by several given names.>