Royal titles follow a long list of traditional rules, some of which can seem quite unusual. According to reports, Louis wasn’t originally guaranteed the title of Prince, despite being born into the royal family.
This comes from a rule introduced during the reign of George V, which limited HRH (His or Her Royal Highness) titles to those closest in line to the throne. Specifically, it applied to the monarch’s children and grandchildren through the male line.
Since Louis was born while Elizabeth II was still on the throne, he didn’t automatically qualify under those rules. The same applied to his siblings, Prince George and Princess Charlotte.
To address this, the late Queen made a special change to the rules, ensuring all of William and Catherine’s children would be granted royal titles. Without that decision, Louis might have been known simply as Master Louis Cambridge or Master Louis Windsor instead.
A similar situation arose for Prince Harry and Meghan Markle when their son Archie Mountbatten-Windsor was born. In their interview with Oprah Winfrey, Meghan shared concerns that Archie might not receive a royal title, and therefore might miss out on certain protections.