Prince William and Kate have named their new-born baby boy George Alexander Louis, William's office said on Wednesday.
The baby, third in line to the British throne, will be known as His Royal Highness Prince George of Cambridge, Kensington Palace said in a statement.
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.
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.
William and Kate were on Wednesday visiting Kate's parents, Michael and Carole, in Bucklebury, southern England.
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