A TWEET from the Kensington Palace Twitter account stated: "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."

With George, the duchess gave birth 10-and-a-half hours after being admitted to hospital, but Charlotte was born just two hours and 34 minutes after Kate arrived at the Lindo Wing.

Press pens are now set to open in front of the hospital to allow media to get in place ready for the birth announcement.

The duchess went on maternity leave on March 22, but was seen at church with the royals on Easter Sunday in Windsor on April 1.

William and Kate chose not to find out whether they were having a girl or a boy at their scan.

The baby prince or princess will be born fifth in line to the throne, the Queen and the Duke of Edinburgh's sixth great-grandchild and a younger brother or sister for Prince George and Princess Charlotte.

The baby's title will be HRH Prince or Princess of Cambridge.