Kate Middleton has been admitted to hospital and is in the early stages of labor, Kensington Palace has said.
The Duchess of Cambridge, who is thought to be one week overdue, travelled by car from the palace to St Mary’s in Paddington, west London, with her husband the Duke of Cambridge.
Prince William and Kate Middleton do not know the sex of their first child, who will be third in line to the throne.
Royal vehicles were seen at a back entrance to the hospital at about 06:00 BST, with the announcement coming from Kensington Palace an hour-and-a-half later.
Kate Middleton is being tended by a top medical team led by the Queen’s former gynaecologist Marcus Setchell, who delivered the Countess of Wessex’s two children.
The couple announced they were expecting their first child in December after the duchess was admitted to hospital suffering from severe morning sickness.
Since the announcement, Kate Middleton has carried out 19 days of public engagements before going on maternity leave in the middle of June.