"We could not be happier," Prince William said after his wife, Kate, the Duchess of Cambridge, gave birth to their son Monday.
The highly anticipated royal baby was born in the private Lindo wing of St. Mary’s hospital in London. The eight-pound, six-ounce boy was born at 4:24 p.m. London time Monday.
Kensington Palace officials said Prince William was present at the birth and that "Her Royal Highness and her child are both doing well and will remain in hospital overnight."
"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," the palace statement said.
The baby's name is not expected to be publicly known for several days.
Kate was admitted to hospital at 6 a.m. BST Monday after a short trip by car from Kensington Palace with William.
Their newborn son is third in line to the throne, following his grandfather Prince Charles and Prince William. The arrival of the new heir to the throne pushes William's brother, Prince Harry, to fourth in the line of succession.
"I think most people are delighted that the baby is healthy," said Dickie Arbiter, former press secretary to the Queen. "May be a little bit of disappointment — they might have wanted to see William and Catherine have a daughter, but it doesn't really matter."
"What it does do, it ensures the succession for three generations of monarchs… For the next three generations, we're going to have kings," Arbiter said.
Before the birth, William and Kate, who were married in 2011, had said they were unaware of the child’s gender. Published reports claimed the couple had purchased many baby items in neutral colours, avoiding the traditional pink and blue hues.
The Queen, who was the first person to be officially notified of the birth, received the news at Buckingham Palace.
William and Kate's baby is the third great-grandchild for the Queen and Prince Philip. Princess Anne's son, Peter Phillips, and his Canadian wife, Autumn, have two daughters.
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Prince Charles said he and Camilla, the Duchess of Cornwall, were overjoyed at the arrival of Charles's first grandchild.
"It is an incredibly special moment for William and Catherine and we are so thrilled for them on the birth of their baby boy," Charles said in a statement issued through Clarence House.
"Grandparenthood is a unique moment in anyone's life, as countless kind people have told me in recent months, so I am enormously proud and happy to be a grandfather for the first time and we are eagerly looking forward to seeing the baby in the near future," Charles said.
He was on official duty in Yorkshire, more than 320 kilometres from London, on Monday as Kate went into labour.
The public was officially informed by the traditional method of posting a paper notice on an easel displayed outside of Buckingham Palace.
Large crowds gathered outside the palace, some pressing up against the fence to get a look at the notice.
"It's a crazy atmosphere. Everyone is getting very excited," said Andrew Aitchison, 47, outside the palace. "It's great to be part of history, to say we were here and saw it all happen."
The birth announcement set off celebrations.
At the Old Boot Inn in Kate's hometown of Bucklebury in southern England, landlord John Haley hosted a party in honour of the new royal baby.
"I think we've had 30 bottles of champagne so far," said Haley, a friend of William and Kate who attended their 2011 wedding.
"We're just over the moon," Haley said.
Said U.K. Prime Minister David Cameron: "It is an important moment in the life of our nation but I suppose, above all, it's a wonderful moment for a warm and loving couple who've got a brand new baby boy."
A 62-gun salute is planned for Tuesday at the Tower of London, along with a 41-gun salute in London's Hyde Park.
"Canadians are delighted to learn of the birth of The Duke and Duchess of Cambridge's son, and we offer our heartfelt congratulations to the Royal Couple and the entire Royal Family," said Canadian Prime Minister Stephen Harper.
"The arrival of the newest member of the Royal Family, a future sovereign of Canada, is a highly anticipated moment for Canadians given the special and warm relationship that we share with our Royal Family.
To mark the royal birth, the CN Tower, Niagara Falls and the Peace Tower on Parliament Hill will all be bathed in blue lights on Monday night.
Settling into role of parents
Officials have said William plans to take two weeks of paternity leave and then return to his military duties as a Royal Air Force search-and-rescue helicopter pilot in Wales.
His tour of duty is scheduled to wrap up in about two months.
It’s not clear where the royal couple will spend their first few weeks with their baby. They have been living in a two-bedroom property on the grounds of Kensington Palace and have been due to move into larger quarters there.
But major refurbishment work on Apartment 1a — where Princess Margaret once lived — likely won't be finished until at least a month or two after the royal birth, and there have been unconfirmed reports Kate and the baby might spend some time with her parents at their home in Bucklebury, west of London.
Come autumn, however, the family will be able to move into their permanent Kensington Palace home — a four-storey apartment with a nursery, 20 rooms and a private garden.
With files from The Associated Press
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