William and his wife, Kate, leaving a London hospital with their baby son.
The press secretary to Britain's Queen Elizabeth, Ailsa Anderson, and footman Badar Azim, place a notice formally announcing the birth of a son to Prince William and Catherine, Duchess of Cambridge, in the forecourt of Buckingham Palace, in central London. (Reuters)
Kate, 31, gave birth to the couple's first child, who is third in line to the British throne, on Monday afternoon, ending weeks of feverish anticipation about the arrival and surprising royal watchers, who were widely expecting a girl.
The baby's name will be announced later but George and James, both traditional royal names, were favoured choices with British bookmakers for the child, who could one day be king.
The popular couple sidestepped tradition by announcing the birth via a press release but were expected to adhere to protocol by giving the public the first sight of the royal baby on the steps as they leave St. Mary's Hospital in west London.
"All we will probably see is a glimpse of the top of the baby's head but they will stick to this tradition," said Joe Little, managing editor of Majesty magazine.
"After that we won't see them for some time. Having a baby is a very private moment and they are a private couple so the next time we see the baby will be the official photo and that could be weeks."
Kensington Palace announced the arrival of a boy weighing 8 lbs 6 oz (3.8 kg) at about 8:30 p.m. (1930 GMT) on Monday, four hours after his birth, saying Kate and her child were doing well and would remain in hospital overnight. Prince William was with them.
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Their son is third in line to the throne after grandfather Prince Charles and father Prince William, 31, and pushes the fun-loving Prince Harry, William's brother, into fourth place.
Kensington's statement announcing the birth of a baby boy to the Deku and Duchess of Cambridge.
Boost for Britain
Congratulations flooded in from all over the world after the announcement of the birth, which was followed moment-by-moment by the world media as well as the British press with the excitement seen as a boost for Britons facing economic austerity.
British tabloid newspaper The Sun temporarily renamed itself The Son in honour of the baby while the left-leaning Guardian newspaper provided readers of its website with a "Republican" button so that they could filter out the barrage of royal news if they wanted.
The birth fuels a new wave of popularity for the House of Windsor led by the younger royals, William and Harry, who were both born to the late Princess Diana at St. Mary's Hospital.
Support for the royals dipped after Diana's death in a car crash in Paris in 1997, a year after her divorce from Prince Charles, as the royals were accused of being out of touch with modern Britain in the way they handled the death of the popular princess.
But last year's celebrations of Queen Elizabeth's 60th year on the throne showed the affection with which she is held by most of the population despite a small Republican movement.
Britain's ministry of defence shows crew members of the British warship HMS LANCASTER celebrating the birth of Prince William and Kate's baby whilst on patrol in the Caribbean. (AFP)
Hordes of TV crews and photographers, and royal fans wrapped in Union Jacks, remained camped outside the hospital overnight Monday, waiting for the first photo of the baby, who will be called the Prince of Cambridge.
Read more: Celebs on Twitter congratulate William, Kate on birth of royal baby
Prince William and Kate, who met when they were students at St. Andrews University in Scotland about 10 years ago, have officially been known as the Duke and Duchess of Cambridge since their sumptuous royal wedding in April 2011.
Tourists in London were reveling in the celebrations that top a run of British sporting victories and an unusual heatwave.
"For me it's a wonderful, historic event. You spend a lot of time studying these things. To actually get to be here to witness one is tremendous," said George Boudreau, 48, a history professor from Philadelphia, outside Buckingham Palace.
Visitors to Niagara Falls receive notice of the sex of the royal baby indicated by the blue light illuminating the falls in Niagara Falls, New York. (AFP)
Britain's Kate and baby boy 'doing well': palace
Britain's Prince William and his wife Kate thanked hospital staff after the birth of their son, as Kensington Palace said the three royals were all "doing well".
"Mother, son and father are all doing well this morning," a Kensington Palace spokesman said in a statement.
In the first comments from Kate since the birth on Monday, she and William said: "We would like to thank the staff at the Lindo Wing and the whole hospital for the tremendous care the three of us have received.
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"We know it has been a very busy period for the hospital and we would like to thank everyone -- staff, patients and visitors -- for their understanding during this time."
Royal officials said the couple and their baby were expected to leave the hospital either on Tuesday after 17: 00 GMT, or on Wednesday.
Chelsea pensioners pose for photographs with a soft toy dressed in their traditional scarlet uniform which will be a gift to the Prince William and Kate's baby boy. (Reuters)
British press revels in royal arrival
Top-selling British newspaper The Sun today changed its name to "The Son" to honour the arrival of a baby boy for Prince William and his wife Kate. For more read: British press marks occasion with souvenir editions
The rest of Fleet Street marked the occasion with souvenir editions, with The Daily Telegraph, The Daily Star and The Daily Express all splashing the headline "It's a Boy" across front-page photographs of the new mother.
The Guardian provided readers of its website with a 'Republican' button so that they could filter out the barrage of royal news if they wanted.
Royal baby adds extra sense of history at Buckingham palace
From Kate-William courtship to the royal baby, a timeline