The Duke of Cambridge signed the birth register as simply "William" at Kensington Palace, witnessed by a registrar.
William and Kate's occupations are listed as Prince and Princess of the UK on the document.
Interestingly, when William's own birth certificate was signed in 1982, there was no box for Princess Diana's occupation. The mother's occupation was not introduced to birth certificates until 1984. Their infant son, who was born on July 22, holds the official title His Royal Highness Prince George of Cambridge.
The couple announced that they had named their bundle of joy George Alexander Louis two days after his birth. Prince George, who weighed 8lb 6oz, came into the world at 4:24 p.m., London time, in the Lindo Wing of St. Mary's Hospital, Paddington.
Celebrations were rife across London, the UK and the rest of the world, as people toasted the birth of the future King who is third in line to the throne.
The couple's baby boy is not the first Prince George of Cambridge. Prince George of Cambridge, born in 1819, was the colourful grandson of King George III, and also held the title. He outraged his cousin Queen Victoria by marrying without her consent and having several illegitimate children. His father was Adolphus, Duke of Cambridge, the seventh of the King's sons, while his mother was Princess Augusta of Hesse-Cassel.
The couple also had two girls Princesses Mary and Augusta of Cambridge. On his father's death in 1850 George inherited the dukedom. He is related to the current Queen through his sister Mary. Her daughter was Queen Mary, who married George V and became Queen Elizabeth II's grandmother.
On Prince George of Cambridge's death in 1904, the title became extinct since he had no legitimate heirs. It was revived in 2011 when his sister's great-great-great-grandson William was created Duke of Cambridge on his wedding day by the Queen.
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A version of this article appeared at hellomagazine.com with the headline "William and Kate have formally registered the birth of Prince George."