The new prince has a name — in fact three.
The infant son of the Duke and Duchess of Cambridge has been named Louis Arthur Charles, Kensington Palace announced Friday.
The palace said the baby's full title is His Royal Highness Prince Louis of Cambridge.
William and Kate's third child was born Monday, a brother to 4-year-old Prince George and Princess Charlotte, who is almost 3.
Louis — pronounced LOO-ee — is fifth in line to the throne after his grandfather Prince Charles, his father and his older siblings.
The name pays tribute twice over to Prince Charles, who has Arthur as one of his middle names.
The choice also honors Louis Mountbatten, Charles' great-uncle and beloved mentor, who was killed by an Irish Republican Army bomb in 1979.
The baby is Britain's first Prince Louis in more than a century.
Mountbatten, a great-grandson of Queen Victoria, was His Serene Highness Prince Louis of Battenberg until 1917, when the royal family anglicized its names to avoid anti-German feeling during World War I. He became Lord Louis Mountbatten.
Britain has never had a King Louis, but France had 16 of them before the country's 1789 revolution.
Bookmakers had been doing a brisk trade in bets on the new prince's name, but Louis wasn't among the favorites. The royal couple has used it before, as one of George's middle names.
Arthur, Albert and James had been considered front-runners.
Twitter users with personal connections to the fresh prince's names offered peals of joy.
Author J.K. Rowling's digital publishing company Pottermore noted that the Weasley family in the Harry Potter books had members named Louis, Arthur and Charles.
"Louis Arthur Charles, you were named after three iconic Weasleys," the company tweeted.
England's Blackpool Zoo announced that a baby Bactrian camel born on the same day as Louis has been named in his honor.
Former One Direction star Louis Tomlinson — a noted devotee of the Adidas brand — tweeted: "Young Louis welcome to the world. I'll take you under my wing lad. The Adidas tracksuit is in the post!"