Choose between public duty and private identity
Royal status can turn a personal relationship into a question of succession, allegiance, or public responsibility. Read whether the protagonist already holds authority, is expected to inherit it, or keeps a royal identity concealed. Those positions create different kinds of freedom and risk within the premise.
Are all royalty stories historical or fantasy?
No. A royal premise can appear in several kinds of setting, including an imagined contemporary one. Historical and Fantasy describe other aspects of the story. Check those genre tags and the original synopsis before assuming a particular time period, political system, or set of supernatural rules.