British monarchs can choose a different name for themselves, known as the Regnal Name (or ruling name) when they ascend the throne. According to the Royal Central, a regnal name differs from the one they received at birth to identify the monarch during their reign. Reader’s Digest goes on to note that there have been many opinions as to the name Prince Charles will choose when he becomes king, and many believe it to be King Charles III’s name. The new king’s government name will also include a government number. Each number is a Roman numeral, making the ruler’s name unique. Confused? Continue reading.
Royal Central speculates that Charles could choose a different name as the two previous monarchs named King Charles were part of the English Civil Wars. The name could bring bad luck! The Prince of Wales has four first names, Charles Philip Arthur George, so he could pick one of those and become King Philip, King Arthur etc – you get the idea. As for his mother, hello! The magazine recalled a story about Elizabeth when she chose her regnal name. When the 25-year-old princess was asked what she wanted her royal name to be, the always sensible Elizabeth replied, “My own, of course.” That’s how Queen Elizabeth II became.
https://www.thelist.com/960590/heres-the-name-charles-is-expected-to-choose-when-he-becomes-king/ Here’s the name Charles is expected to choose when he becomes king