The Duchess of Cambridge has given birth to a new baby boy, Kensington Palace has announced.
Catherine and Prince William welcomed the new baby on Monday, the couple's third child who is fifth in line to the British throne.
The boy, weighing eight pounds and seven ounces (3.8 kilogrammes), was born at 11.01am (1001 GMT), Kensington Palace announced.
Mother and baby are both doing well, the palace said, and William, the Duke of Cambridge, was present for the birth.
The baby is the couple's third child, after Prince George and Princess Charlotte.
Queen Elizabeth II, William's father Prince Charles, and his brother Prince Harry were said to be delighted with the news.
"Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 11.01 hours," the palace announced in its brief statement.
Kate, 36, was admitted early Monday to the private Lindo Wing of St. Mary's Hospital in central London, where four-year-old George, and Charlotte, aged two, were born.
Royal fanatics, who had been camped outside the hospital wing for several days in anticipation, jumped for joy and popped open champagne.
"We're going to celebrate with fish and chips!" said John Loughrey, who was wearing a Union Jack hat and clutching a plastic doll with a crown.
Maria Scott, 46, a housewife from Newcastle in northeast England, has been in place for 15 days.
"It's really important to show support because they need to know how much they are loved by the people," she told AFP.
"We're very proud of our monarchy."
Tony Appleton, a town-crier dressed in a flamboyant red uniform, announced the news from the steps of the hospital's Lindo Wing to a crowd of supporters and media.
The baby was born on St. George's Day, England's national day.
The baby boy is a sixth great-grandchild for Queen Elizabeth, who turned 92 on Saturday, and her husband Prince Philip. It will hold the title of prince after Queen Elizabeth changed the rules in 2012 to ensure that all of William's children would be entitled to the style, not just his eldest son.
As with their two previous children, the royal couple did not know whether the baby was going to be a boy or a girl. Bookmakers have Arthur, Albert, Frederick, James and Philip as their favourites for the young prince's name.
The boy does not overtake Charlotte in the line of succession due to new laws agreed across the 16 Commonwealth realms where Queen Elizabeth is the head of state, including Canada, Australia and New Zealand. Under the law, designed to end male primogeniture for William's children, boys born after October 28, 2011 cannot overtake their elder sisters.
A night at the Lindo Wing costs £7,500 (US$10,500, 8,550 euros), including a delivery package and two-room suite, excluding consultants' fees.
The birth was overseen by consultant obstetrician Guy Thorpe-Beeston, who is the surgeon gynaecologist to the royal household, and consultant gynaecologist Alan Farthing, the Queen's surgeon-gynaecologist.
They were part of the trusted team who also delivered George and Charlotte.
The duchess suffered severe morning sickness during all three pregnancies.
Gun salutes planned
William, who is destined to become king after Charles, and Kate met at St. Andrews University in Scotland.
They tied the knot at Westminster Abbey in London on April 29, 2011, in a ceremony watched by up to two billion people worldwide. The marriage helped breathe new life into Britain's monarchy after years of crisis.
The Sun newspaper reported Sunday that Kate's sister Pippa Middleton, 34, is pregnant with her first child. Kate's maid of honour famously stole the show at her and William's wedding with a figure-hugging dress.
The birth will be celebrated with a 41-gun salute in London's Green Park Hyde Park – the standard 21 rounds with an extra 20 because they are royal parks. The Tower of London will fire 62 rounds: 21, plus 20 because it is a royal palace, and a further 21 to show the City of London's loyalty to the sovereign.
Line of succession
Prince William and his wife Kate's baby is fifth in line to inherit the British throne, behind big brother Prince George and sister Princess Charlotte.
The immediate line of succession to the throne includes Queen Elizabeth II's four children and their descendants:
1. PRINCE CHARLES, PRINCE OF WALES
-- Born 1948, eldest son of Queen Elizabeth
2. PRINCE WILLIAM, DUKE OF CAMBRIDGE
-- Born 1982, Charles's eldest son
3. PRINCE GEORGE OF CAMBRIDGE
-- Born 2013, William's son
4. PRINCESS CHARLOTTE OF CAMBRIDGE
-- Born 2015, William's daughter
5. BABY PRINCE OF CAMBRIDGE
-- Born on Monday
6. PRINCE HENRY OF WALES (PRINCE HARRY)
-- Born 1984, Charles' second son
7. PRINCE ANDREW, DUKE OF YORK
-- Born 1960, Queen Elizabeth's second son
8. PRINCESS BEATRICE OF YORK
-- Born 1988, Andrew's eldest daughter
9. PRINCESS EUGENIE OF YORK
-- Born 1990, Andrew's second daughter
10. PRINCE EDWARD, EARL OF WESSEX
-- Born 1964, Queen Elizabeth's third son
11. JAMES, VISCOUNT SEVERN
-- Born 2007, Edward's son
12. LADY LOUISE WINDSOR
-- Born 2003, Edward's daughter
13. PRINCESS ANNE, PRINCESS ROYAL
-- Born 1950, Queen Elizabeth's daughter
14. PETER PHILLIPS
-- Born 1977, Anne's son
15. SAVANNAH PHILLIPS
-- Born 2010, Phillips' eldest daughter
16. ISLA PHILLIPS
-- Born 2012, Phillips' second daughter
17. ZARA TINDALL
-- Born 1981, Anne's daughter
18. MIA TINDALL
-- Born 2014, Tindall's daughter
Queen Elizabeth's descendants are followed by those of her late sister princess Margaret, her only sibling.
The offspring of their father king George VI's siblings then follow. There are more than 60 living people descended from his father king George V, who died in 1936. Only people descended from Sophia of Hanover can inherit the throne, according to the 1701 Act of Settlement.
The monarchy's website goes down as far as Zara Tindall, though some counts list more than 5,700 living descendants of Sophia, including Roman Catholics, who cannot inherit.
The highest excluded person is 26-year-old Edward Windsor, Lord Downpatrick, a first cousin twice removed of the queen, who converted to Catholicism. He would otherwise be 37th in line after the new baby is born.
In changes to the succession laws which came into effect in 2015, males born after October 28, 2011, no longer take precedence over their older sisters.
Also people married to Catholics are no longer excluded, with Downpatrick's father George Windsor, the Earl of St Andrews, the highest person restored to the line.
The line is a vast tangle of nobility and ordinary, untitled descendants from all corners of Europe. Several other European monarchs feature. Besides Britain, it is also the line of succession to the thrones of 15 other Commonwealth realms.