Kate Middleton has given birth to a baby boy, Kensington Palace has confirmed.
Kate's baby arrived at 11.01am, and weighed in at 8 pounds and 7 ounces.
Britain's Prince William was beside her for the birth. They are both doing well, and the Royal family are said to be delighted.
Kensington Palace said: "Her Royal Highness the Duchess of Cambridge was safely delivered of a son at 1101hrs.
"The baby weighs 8lb 7oz. 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.
"Her Royal Highness and her child are both doing well."
Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs.
The baby weighs 8lbs 7oz.
The Duke of Cambridge was present for the birth.
Her Royal Highness and her child are both doing well.— Kensington Palace (@KensingtonRoyal) April 23, 2018
Kate was taken to the private Lindo Wing at St Mary's Hospital in Paddington, London, before 6am this morning in the early stages of labour, with Prince William at her side.
The baby is fifth in line to the throne, the Queen and the Duke of Edinburgh's sixth great-grandchild and a younger sibling of Prince George and Princess Charlotte.
The baby's sex was a surprise to William and Kate, who chose not to find out what they were having.
Kate will be expected to head home to the sanctuary of Kensington Palace in a few hours, just as she did with Charlotte in 2015 - but not before introducing the new royal baby to world on the steps of the Lindo Wing.
George and Charlotte might even visit the hospital to see their mother and baby sibling, just as George did when his younger sister was born three years ago.
The new royal baby has been born on St George's Day which celebrates the patron saint of England, and arrived just two days after the Queen's 92nd birthday.
The baby's title is His Royal Highness and he is a Prince of Cambridge.