Louis was the first name of the Prince of Wales' beloved great-uncle Earl Mountbatten of Burma.
Charles will be touched that the Duke and Duchess of Cambridge decided to pay tribute to Lord Mountbatten, who was murdered by the IRA in 1979, by naming their son Prince Louis.
The name, also one of Prince George's middle names, is French and German in origin and means "renowned warrior".
Louis was the 71st most popular name in England and Wales, according to the latest available figures from the Office for National Statistics.
In 2016, just 911 boys were given the name Louis in England and Wales.
It was more popular in the early 2000s when it ranked around 39th, but was not popular throughout the 20th century.
Louis has been the name of many rulers across the world, including 18 kings of France.
Famous people named Louis include pop star Louis Tomlinson from One Direction and jazz trumpeter Louis Armstrong.
Lord Louis Mountbatten was also the Duke of Edinburgh's uncle and the brother of Philip's mother Princess Alice.
He was the last British Viceroy of India before independence in 1947.
He was very close to Charles but Uncle Dickie, as he was known in the family, was assassinated by the IRA in August 1979.
His boat was blown up on a fishing trip off the coast of County Sligo in the Republic of Ireland.