Prince Louis turns seven today (April 23) and it appears some fans of the Royal Family are only just learning who the youngster was named after.

The youngest child of Prince William and Princess Catherine was born Louis Arthur Charles Mountbatten-Windsor at London's St. Mary's Hospital in 2018. Whilst his third name, Charles, is an obvious nod to his grandfather, it's Louis and Arthur that are the more intriguing monikers.

In fact, we have to go as far back as 1900 to discover the origins of Louis' Christian name. One TikTok user points out that Louis is named after Lord Louis Mountbatten - the maternal uncle of the late Prince Philip, Duke of Edinburgh and second cousin of King George VI. 

Lord Mountbatten was killed in an IRA attack in Mullaghmore, County Sligo, Ireland in 1979, which saw a bomb planted on board his fishing boat. Royal historian Robert Lacey previously explained to People: "It shows the romance of this name associated with the hero and family mentor whom William never met - his father's 'honorary grandfather'."

Indeed, Lord Mountbatten had been somewhat of a mentor to King Charles III, a frequent prescence during his childhood, but died five years before Prince William's birth.

Arthur, meanwhile, is a middle name Prince Louis shares with his father (Prince William Arthur Philip Louis), grandfather (King Charles Philip Arthur George), and great-grandfather (Albert Frederick Arthur George - King George VI). While never confirmed by the royals, it is widely believed Arthur is a nod to mythological medieval King Arthur. 

Arthur has been a royal name for hundreds of years, and the country almost had a King Arthur back in the 16th century. Arthur was the eldest son and heir of King Henry VII. However, he died as a teenager, paving the way for his younger brother, Henry to take the throne and go on to become King Henry VIII.

"I find it cute how all the children has Charles in their name or someone linked to their family," one TikTok user penned in response. On Reddit, another added: "Oh, I love it! I’m surprised they went with Louis because it’s already one of Prince George’s middle names, but I think it’s much nicer than Albert/Arthur/Alfred which seemed to be the top guesses."

Meanwhile a third person admitted: "It certainly strikes me as odd especially as it is predominantly associated with the French." And a fourth concurred: "That was exactly what I was thinking! I feel like it is super strange since so often in English history Louises (I guess that's how you make that name plural?) were rivals of English kings."

When Prince Louis was born, his great-grandmother, Queen Elizabeth II had to overturn a historic rule implemented by King George V in order to make sure he had a royal title. Back in 1917 George V decided that only children of the sovereign would become a Prince or Princess upon birth, as well as any grandchildren born through the male line.

However, when Prince William and Princess Kate had their family, the late Queen made sure they would all receive their HRH titles by changing the 100-year-old rule. If that had not been the case, Louis would have been known by a different name entirely, as Master Louis Cambridge when he was born or Master Louis Windsor now.