PRINCE William and wife Catherine have named their new baby Louis Arthur Charles in a twist that has shocked British punters.
After days of anxious waiting for royal watchers, Kensington Palace put out statement at 11am local UK time Friday revealing that Catherine and William's third child had been named Louis Arthur Charles.
"The Duke and Duchess of Cambridge are delighted to announce that they have named their son Louis Arthur Charles," the Kensington Palace statement said.
"The baby will be known as His Royal Highness Prince Louis of Cambridge."
The choice has come as surprise to royal watchers who had ruled out Louis as an option because it is one of the middle names of Prince George.
Punters in England had been placing bets right up until the moment the name was announced by Kensington Palace.
Across all major agencies Arthur had the best odds for a first name with Albert, James, Frederick and Philip also proving popular.
For punters who placed a $1 bet on the name Louis yesterday morning they will getting a whopping $33 back.
The name is a nod to both Prince Philip's grandfather Prince Louis Alexander of Battenberg and uncle Earl Louis Mountbatten who was assassinated by the IRA in 1979.
Louis is also one of William's middle names.
Charles is an obvious tribute to William's father, whereas Arthur is also one of the middle names of both Charles and William.
A spokesperson from betting agency William Hill told News Corp they taken about $AUD280,000 worth of bets on the new baby name.
Arthur was the most popular guess representing 4000 bets, Henry was the least raking up just six per cent of all guesses.
Royal commentator Victoria Howard told News Corp the couple would have run the name past the Queen.
"I'm sure William will have run it by the Queen to check she think it's appropriate," Ms Howard said.
"They like to draw on that family link and history of the British monarchy when they choose names."
The name Louis is likely to climb up in the ranks of the most popular annual baby names' now it has been given the royal seal of approval.
Following the birth of Prince George in 2013 and Princess Charlotte in 2015 both names have jumped in popularity.
"Both George and Charlotte saw a surge of popularity once they were revealed as royal baby names and it's likely that we will see that again," Ms Howard said.
George was the third most popular boy's name in the UK in 2016 and Charlotte climbed to the 12th most popular girl's name.
Prince Louis is fifth in line to the throne and was born at 11:01am UK local time on Monday at St Mary's Hospital in Paddington, London.
Believed to be the biggest royal baby in more than 100 years he weighed 3.8kg.