The names of westerners are different from those of China. China people pay attention to taboos, and the words in their elders' names must not be used. However, westerners will use the names of elders they like or respect. So the names of father and son or grandson will be the same. Napoleon's full name is Napoléon Bonaparte, Napoleon is his first name and Bonaparte is his last name. Among his ancestors, there are already two Napoleon, so in order to distinguish who is who, he is called III.
It has nothing to do with whether you are a king or not, just to distinguish yourself from your ancestors.