Prince William and his wife Kate, the Duke and Duchess of Cambridge, are expecting a baby in April 2015, ABC News quoted Palace officials as saying in a press release.
Kate continues to be affected by acute morning sickness, but her condition is steadily improving, according to the release.
Her pregnancy was announced in September, after she was forced to skip a number of public events.
The baby will be the second for the royal couple, joining 1-year-old George. The baby will be fourth in line to the British throne after grandfather Prince Charles, father Prince William and big brother George.
It is playfully called "an heir and a spare," with George in direct line to the throne and the new baby his alternate. Second-born royal babies can end up as monarch. Britain’s last King, George VI, acceded to the throne in 1936 when his older brother Edward VII abdicated.