The Duke and Duchess of Cambridge have named their son George Alexander Louis, Kensington Palace has said.
The third in line to the throne, who was born on Monday at 16:24 BST, will be known as His Royal Highness Prince George of Cambridge.
It is thought the Queen was told of Prince George’s name when she met him for the first time on Wednesday.
The family are at the Middleton home in Bucklebury, Berkshire, after spending a night at Kensington Palace.
George was the bookmakers’ favourite for the first name of the prince.
The duke and duchess had been expected to pick a traditional royal name for their son, who was born at St Mary’s Hospital in London, weighing 8lbs 6oz.
Royal infants usually have historical names which are passed down through the generations.
There have been six King Georges up to now, most recently the Queen’s father, although his first name was Albert and he was known to his family as Bertie.
The name Louis is Prince William’s fourth name and is likely to be a tribute to Lord Louis Mountbatten, the Duke of Edinburgh’s uncle and the last British Viceroy of India before independence in 1947.
Lord Mountbatten and William’s father the Prince of Wales were very close. Known by the Royal Family as Uncle Dickie, he was assassinated by the IRA in August 1979.
BBC royal correspondent Nicholas Witchell said Alexander was said to be a favourite of Catherine’s.
The BBC’s Peter Hunt said the Queen’s middle name is Alexandra and it is assumed the baby has been named after the Queen’s father.
Our correspondent also said Prince George does not have to be King George if he accedes to the throne – he can choose another name, as the Queen’s father did. (BBC)