Catherine, the Duchess of Cambridge, has gone into labour.
The 36-year-old royal - who already has son Prince George, four, and daughter Princess Charlotte, two, with husband Prince William - was admitted to hospital on Monday morning in preparation for welcoming her third child into the world.
A statement released by Kensington Palace said: "Her Royal Highness The Duchess of Cambridge was admitted to St. Mary’s Hospital, Paddington, London earlier this morning in the early stages of labour.
"The Duchess travelled by car from Kensington Palace to the Lindo Wing at St. Mary’s Hospital with The Duke of Cambridge."
Catherine - who was known as Kate Middleton before her marriage - carried out her last official royal engagement last month at the Team SportsAid event in London and will be on maternity leave until the autumn.
READ: Prince William 'supportive' of Catherine's home birth dreams
An insider said recently: "Kate is now officially on maternity leave until the autumn and looking forward to welcoming the new baby.
"The whole family is excited, including the children, who are very much aware that they are about to welcome a new brother or sister."
The duchess' first stop on maternity leave was to spent Easter with her parents Michael and Carole Middleton in
Bucklebury, Berkshire, England, with her family before settling back home in London as her due date approached.
A source said at the time: "Kate is in Bucklebury with the children for the Easter weekend, putting her feet up and enjoying some well-earned rest.
"The children are on Easter holiday now so they'll all stay at Carole and Michael's into the middle of next week and then return to Kensington Palace, where Kate will remain until she goes into labour. William may be back and forth due to work."
The royal couple were forced to announce their third pregnancy earlier than they would've liked last year because Catherine was battling with hyperemesis gravidarum - a severe form of morning sickness - and was forced to pull out of engagements.