It is understood that Queen Elizabeth II intervened to alter the name of Prince Louis.
The news comes to light as the mini royal looks to celebrate his fourth birthday on Saturday 23 April 2022.
Louis was born in the Lindo Wing of St Mary’s Hospital, a fancy exclusive maternity ward in Paddington.
His parents, the Duke and Duchess of Cambridge, mirrored Prince Charles' decision, with choosing the venue for all three of their three children's births.
Louis is the youngest of three siblings and is fifth in line to the throne.
He was born on St George’s day on April 23 2018, weighing 8lb 7oz, according to the Scottish Daily Express.
He was christened Louis Arthur Charles at 11 weeks old, by the Archbishop of Canterbury Justin Welby at the Chapel Royal, St James's Palace in front of friends and family.
But despite being in line for the throne, it is little known how it was unlikely the children would be titled prince or princess if it weren't for the actions of the Queen.
Several days after birth it was revealed that Prince William and Kate would be naming their youngest son Louis Arthur Charles.
But his official princely title is only possible because Her Majesty overwrote a rule made by her grandfather King George V, reports the Express.
In 1917, he set out new guidance on which royals were allowed to have titles; deciding all of the sovereign's children would automatically become a Prince or Princess, as well as any grandchildren born through the male lineage.
But great-grandchildren were deemed too far down the line to qualify.
The Queen stepped in to change the rules saying Prince George would get a title as well as any children after him.
If she hadn't it's more likely the birthday boy prince would have been named Master Louis Cambridge or Master Louis Windsor instead.
But the rule does not apply to the Cambridge royal's cousins; for this reason the children of the Queen’s daughter, Princess Anne, were not entitled to be known as Prince or Princess.
It comes as little Prince Louis has been photographed barefoot, laughing and ready for a game of beach cricket in a series of images taken to mark his fourth birthday.
The young prince has been attending Willcocks Nursery School near his Kensington Palace home for more than a year and is likely to celebrate his birthday with school friends and family.
Louis has rarely been seen in public and one of his most prominent outings was when he joined his parents and siblings, Prince George and Princess Charlotte, at a special pantomime performance at London's Palladium Theatre in December 2020.
