"The duke and duchess of Cambridge are delighted to announce that they have named their son George Alexander Louis," the Twitter message said Wednesday. "The baby will be known as His Royal Highness Prince George of Cambridge."
The little prince was born Monday after 14 hours of labor and a natural delivery. He left St. Mary's hospital in London with his father Prince William and mother Kate Tuesday night.
Upon leaving the hospital, William confessed to the crowd gathered outside that he and his wife were still "working on a name."
The child's name was officially announced Wednesday, the same day the prince and his parents visited the country estate of his maternal grandparents, the Middletons, in Bucklebury, following a drop-by from his great-grandmother, Queen Elizabeth II, at the family's Kensington Palace apartment.
It was the first visit of a reigning monarch to a future king three generations down the line in 120 years, The Daily Telegraph reported.
If he ascends to the throne, the little prince will be known as King George VII. Elizabeth's father was George VI.
William's brother, Prince Harry, visited the new family, dropping off a card from well-wisher Amanda Winney, 49, who included a 10-pound note she said he hoped would be used to buy a stuffed animal, the Telegraph said.
Prince George is third in line to the throne behind William and Prince Charles, who is the current monarch's direct heir.