George Alexander Louis is the name of The Duke and Duchess' baby son.
Clarence House tweeted: "The Duke and Duchess of Cambridge are delighted to announce that they have named their son George Alexander Louis. The baby will be known as His Royal Highness Prince George of Cambridge."
The name George had topped the list of betting sites, followed by James.
There has been six King George's until now and Queen Elizabeth's father was named George, although he was known as Bertie.
Alexander is said to be The Duchess' favourite choice, and Louis is Prince William's fourth name.
Following the descendants of Queen Elizabeth II and Prince Philip, Prince William's surname is Mountbatten-Windsor, and that is also the name Catherine, Duchess of Cambridge.
Queen Elizabeth was seen traveling to Kensington Palce today to see her great-grandson for the first time. Middleton's sister also reportedly met her nephew at the palace yesterday.
The announcement comes a day after The Duke and Duchess of Cambridge showed their baby Prince for the first time outside of the Lindo Wing at St. Mary's Hospital.
The royal couple looked joyous and emotional as they held their baby, giving the world media a first glimpse of the heir to the British throne. Kate Middleton wore a sky blue polka dot dress by Jenny Packham and looked radiant after becoming a first-time mom.
"It's very special," Prince William said to reporters. "He's got her looks, thankfully," he joked.
Prince William said that he and his wife are "still working on a name" for their son. They revealed that the baby had a "good pair of lungs" and that the experience was "very emotional" for them.
"He's got a good pair of lungs on him, that's for sure. He's a big boy, he's quite heavy. We are still working on a name so we will have that as soon as we can. It's the first time we have seen him really so we are having a proper chance to catch up."
The Duchess told reporters: "It's such a special time. I think any parent will know what this feeling feels like."
Prince William also said, "I'll remind him of his tardiness when he's a bit older." He told reporters, "I know how long you've all been standing here so hopefully the hospital and you guys can all go back to normal now and we can go and look after him." They also said that Prince William gave the baby his first nappy change.
The crowd waiting outside cheered as the couple came out. A name has not been announced yet for the Prince, who is now third in line to the throne.
Shortly after speaking to reporters, Kate Middleton and Prince William went back inside the hospital to put their baby inside a car seat. They emerged again, with Prince William carrying the car seat with the baby inside. He installed the car seat in the car with the Duchess before driving off with his new family to Kensington Palace.
Earlier in the day, her parents Carole and Michael Middleton arrived at the hospital to see their first grandson. They told reporters that the royal baby is "absolutely beautiful."
Shortly after, Prince Charles and Camilla arrived for a brief visit.
A 41-gun salute was held by The King's Troop Royal Horse Artillery at Green Park in London to mark the birth of The Duke and Duchess of Cambridge's child today. The Honourable Artillery Company also fired a 62-gun salute from Gun Wharf at the Tower of London at the same time. The church bells of Westminster Abbey also rang out for three hours.
A spokesman for the Kensington Palace has said, "Mother, son and father are all doing well this morning."
Meanwhile, the new parents released a statement thanking staff at St. Mary's Hospital. "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. 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."
President Obama congratulated the couple, tweeting: "So pleased to congratulate The Duke and Duchess of Cambridge on the joyous occasion of the birth of their first child."
The royal family released statements on the joyous birth of the Prince, with his father Prince William saying, "We could not be happier."
The palace released a statement saying that the Duchess and the baby are "doing well" and will stay in the hospital overnight.
Clarence House tweeted: "The Queen and Prince Philip are delighted at the news of the birth of The Duke and Duchess of Cambridge's baby."
Prince Charles of Wales also said in a statement: "Both my wife and I are overjoyed at the arrival of my 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.
"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."
The news of the baby's arrival was first given to the Queen. A bulletin, signed by the Queen's gynaecologist Marcus Setchell, whose team led the delivery of the baby, was taken to Buckingham palace under police escort.
"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 bulletin said.
Prime Minister David Cameron tweeted: "I'm delighted for the Duke and Duchess now their son has been born. The whole country will celebrate. They'll make wonderful parents."
The Duchess of Cambridge checked into St. Mary's hospital with Prince William at 5:30 a.m. yesterday
The pair arrived by car from Kensington Palace to the Lindo Wing at St. Mary's Hospital .
The royal baby will become third in line to the throne, replacing Prince Harry. He will be given the title Prince and will become the future King of Britain.
