The royal baby and third line to the throne has been named George Alexander Louis, royal officials have announced.
The baby will be known as His Royal Highness Prince George of Cambridge, Kensington Palace said in a statement.
George Alexander Louis was born on Monday, prompting an international media frenzy as well as celebratory gun salutes and the illumination of London landmarks in blue.
George has been the name of six British kings. The last, George VI, was the father of Queen Elizabeth and reigned from 1936 to 1952.
Alexandra, the female form of Alexander, is one of the Queen's middle names, and was also the name of the Queen Consort of King Edward VII at the start of the last century.
Louis is one of William's middle names, and was the given name of Prince Charles's mentor and great-uncle Louis Mountbatten, who was assassinated by Irish nationalist IRA guerrillas in 1979.
The announcement of the royal heir's name was relatively quick by royal standards, Reuters reports. It took a month for the name of Prince Charles to be announced and a week for William.