Four days later, the royal couple shared their newest bundle of joy's name -- Louis Arthur Charles.
"The Duke and Duchess of Cambridge are delighted to announce that they have named their son Louis Arthur Charles. The baby will be known as His Royal Highness Prince Louis of Cambridge," the Kensington Royal Twitter feed announced on April 27.
While at an Anzac Day service in London on April 25 before the moniker was shared publicly, William chatted with other attendees and was heard hinting to one that his new son had a "strong name," the Daily Mail reported. William also said the newborn was "sleeping reasonably well so far" and that "he's behaving himself, which is good news."
According to reports published before the announcement, Albert and Arthur were the odds-on name favorites. Britain-based betting and gambling company Ladbrokes had Albert (Queen Elizabeth II's father's given name) at 5-1 odds and Arthur (one of Prince William's middle names) at 9-1 odds, People magazine reported, while Philip (the prince's paternal great-grandfather's name, which is also one of William's middle names) was also in the running at 16-1 odds.
Louis's names are nothing new: Louis itself is one of Prince William's middle names and one of big brother Prince George's middle names. It's also the name of Prince Philip's grandfather, Prince Louis Alexander of Battenberg.
Both William and his father, Prince Charles, share Arthur among their middle names. And Charles, of course, honors the little guy's grandfather.
Kensington Palace announced Prince Louis's birth on Twitter just after 8 a.m. ET on April 23. "Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs. The baby weighs 8lbs 7oz. The Duke of Cambridge was present for the birth. Her Royal Highness and her child are both doing well," the palace tweeted.
Prince Louis is fifth in line to the British throne behind big brother Prince George, 4, big sister Princess Charlotte, 2, dad Prince William, 35, and grandfather Prince Charles, 69.
He arrived two days after his great-grandmother the queen's 92nd birthday on April 21.
Speaking of the monarch, she's "delighted" to have another great-grandchild. "The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, Prince Harry and members of both families have been informed and are delighted with the news," Kensington Palace's Twitter feed announced shortly after the new royal's arrival.
The other young Cambridges also have quite epic monikers. George's full name is Prince George Alexander Louis. The boys' sister's full name is Princess Charlotte Elizabeth Diana.