The third in line to the throne will be called "Georgie in no time," said his grandfather Prince Charles, according to the BBC's Peter Hunt who announced the news on Twitter.
"Prince Charles on his grandson's name: George is 'a very good name', but he'll be called 'Georgie in no time'. #RoyalBaby #princegeorge," wrote Peter.
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Prince Charles was attending the Whitstable Oyster Festival in Kent, accompanied by Camilla, Duchess of Cornwall, when he made the revelation.
The couple were seen walking around the stalls, trying oysters and mingling with fellow festival-goers. Prince Charles was clearly getting ready for his role as a first-time grandfather as he was spotted happily chatting to a mother and small child.
He was also presented with an adorable yellow baby t-shirt for little Prince George, while Camilla was given a Punch and Judy doll as a souvenir of their day at the festival.
The British royal family are known for having endearing nicknames for each other. After Prince William and Kate appeared on the steps of the Lindo Wing last Tuesday to present Prince George to the world, the young father was heard calling his wife "poppet" as he ushered her back inside the hospital.
The Duke of Cambridge tenderly put his hand on his wife's back and affectionately addressed her using the adorable moniker.
As a child, Prince William was called "wombat" by his mother Princess Diana after the family made the trip to Australia and saw the creatures first-hand. When he attended the University of St Andrews in Scotland, Prince William was called "Steve" by his friends.
Kate, meanwhile, was called "Squeak" at school, named after her pet guinea pig.
"I was nicknamed 'Squeak' just like my guinea pig," she said. "There was one called Pip and one called Squeak because my sister was called Pippa and I was Squeak."
When the Queen was growing up, she became known as 'Lilibet' among her family and close friends, and while some of them apparently still use the affectionate nickname for the monarch, her husband Prince Philip's choice is perhaps the most amusing.
His pet name for his wife came to light after the 2006 film The Queen was released, where the Duke of Edinburgh is seen saying, "Move over, Cabbage," in a bedtime scene at Balmoral.