The Duchess of Cambridge has given birth to a baby boy this afternoon.
The baby weighed 8lbs 6oz and was born at 4.24pm, the palace said.
Kensington Palace released an official statement, which read: "Her Royal Highness and her child are both doing well and will remain in hospital overnight."
"The Duke of Cambridge was present for the birth. The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, Prince Harry and members of both families have been informed and are delighted with the news."
Kate Middleton went into labour and was admitted to the private Lindo Wing of St Mary's hospital this morning. Britain has been on tenterhooks today, waiting for news of the royal family's newest addition.
The official notice of birth was taken from St Mary's Hospital and has been placed on an easel outside Buckingham Palace, as is tradition with a royal baby.
The royal baby is now third in line for the throne, having overtaken Prince William's brother, Harry.
News that Kate and William have welcomed a baby boy into the world will come as a surprise to many, including bookmakers, who believed the baby was likely to be a girl.
The birth will be marked with a number of gun salutes at 2pm today (23 July).