The Duchess of Cambridge has given birth to a boy, her third child and second son.
The new arrival, who was born at St Mary’s Hospital, London, is fifth in line to the throne and the Queen’s sixth great-grandchild.
The Duke of Cambridge was present for the birth of his son at 11:01 BST, weighing 8lb 7oz.
A Kensington Palace statement said Catherine and her son, who is yet to be named, are “both doing well”.
Members of both families had been informed and were “delighted with the news”.
Kensington Palace said the name of the baby would be announced in due course while a formal notice of the birth had been posted on the forecourt of Buckingham Palace.
Favourite names at the bookmakers include Arthur, Albert, Frederick, James and Philip.
Prime Minister Theresa May tweeted her “warmest congratulations” to William and Catherine.
She said: “I wish them great happiness for the future.”
The Archbishop of Canterbury added: “Congratulations to The Duke and Duchess of Cambridge on the safe delivery of their baby, a brother for Prince George and Princess Charlotte.
“May God bless them and all of their children with love, happiness and health.”
Mayor of London Sadiq Khan tweeted: “On behalf of Londoners, I want to send our warmest congratulations to the Duke & Duchess of Cambridge on the birth of their baby boy.”
Sir Vince Cable, leader of the Liberal Democrats, said: “Congratulations to the Duke and Duchess of Cambridge on the birth of their son.
“I’m sure his older brother will be delighted he has been born on St George’s Day!”
— The Royal Family (@RoyalFamily) April 23, 2018
Following a change in the law in 2013, Princess Charlotte keeps her place as fourth in line to the throne.
Previously, younger royal males would have taken precedence over older female siblings.
The duchess was admitted to hospital shortly before 06:00 on Monday with the announcement of the birth coming shortly after 13:00.
Senior royal doctors consultant obstetrician Guy Thorpe-Beeston and consultant gynaecologist Alan Farthing oversaw the birth.
Both were also called in for the arrival of Prince George in 2013 and Princess Charlotte in 2015.
The new prince, born on St George’s Day, shares a birthday with Lady Gabriella Windsor – the daughter of Prince and Princess Michael of Kent, who was born at the Lindo Wing on 23 April 1981.
Will the new prince be king?
To become King or Queen as the third-born royal child is rare – and has yet to happen within the current House of Windsor.
But the third child of George III and Queen Charlotte, William IV, took on the task and ruled from 1830 to 1837.
The Hanoverian king acceded to the throne aged 64 when his older brother, George IV, died without an heir.
He became next in line when he was 62 and his other older brother, Frederick, Duke of York, died.