Prince William and his wife Catherine's first child is due in July, St James' Palace announced adding that the mother-to-be is feeling better following her hospitalisation last month.
"Their Royal Highnesses The Duke and Duchess of Cambridge are delighted to confirm they are expecting a baby in July," the palace said in a statement.
Officials refused to give the exact due date but, assuming the Duchess conceived last October, shortly after returning home from her South Pacific tour, the baby is likely to be born towards the middle of the month.
Kate has now had her crucial 12-week scan and doctors have told her the baby is healthy.
The new third in line to the throne will be born under the star sign of Cancer, assuming he or she arrives between June 21 and July 22.
Last week she was photographed attending a performance of the Cirque du Soleil in London for her birthday, and also attended the unveiling of her first official portrait at the National Portrait Gallery, where she looked well.