Kate Middleton and Prince William's son, Prince George Alexander Louis, already has a nickname - even though he is just a week old.
Prince Charles, who was speaking to visitors at the Whitstable Oyster Festival in Kent, said the baby "will be known as Georgie in no time."
Previously the late Prince George, Duke of Kent was also called Georgie by family members.
Charles, who was with wife Camilla, the Duchess of Cornwall, also said that George was "a very good name".
However the 64-year-old said that his grandson is already making a big noise in the royal household.
When asked how the baby was, Charles said: "Oh, wonderful. Very loud, but wonderful," adding: "he's a good boy, he's quite heavy."
Previously, Prince William had revealed that his newborn son has "got a good pair of lungs".
William's wife Kate Middleton gave birth to George, who is third in line to the throne, on 22 July in the Lindo wing of London's St Mary's Hospital.