The Duchess of Cambridge, Kate Middleton, went into labour this morning.

The news by announced in a tweet by Kensington Palace.

The Duchess and Prince William already have two children - Prince George, four, and Princess Charlotte, two.

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.

Favourite names at the bookmakers include Mary, Alice, Alexandra, Elizabeth, and Victoria for a girl and Arthur, Albert, Frederick, James and Philip for a boy.