Kingly, regal, royal, queenly, imperial, princely are comparable when meaning of, relating to, or befitting one who occupies a throne.
Kingly, regal, and royal are often interchanged, especially when used in reference to a monarch who is called king; thus, kingly, regal, or royal power are equally appropriate and idiomatic. However, usage shows a degree of preference for kingly when the reference is to the personal or ideal character of a king or to his feelings, disposition, aims, or actions or for regal when the reference is to the king's office or the state or pomp which accompanies the exercise of his powers and for royal when the reference is to persons or things associated with the king either as a person or as a monarch, but not necessarily involving magnificence or display. In extended use kingly carries the strongest implication of dignity and nobility while regal suggests magnificence or majestic character and royal, fitness or suitability for a king especially in superlative excellence.
Queenly is used in place of kingly when the reference is directly to a person who is a female sovereign in her own right or is the consort of a king. But when the reference is to the office, the family of the queen, or anything to which regal and royal are normally applied, the latter adjectives are used without reference to the sex of the sovereign.
Imperial suggests reference to a monarch who is called emperor or empress. In extended use imperial implies fitness or suitability for an emperor or empress and typically suggests a more awe-inspiring quality than kingly and more pomp and grandeur than regal or royal.
Princely implies reference to one who is called a prince and especially to one who is so called as the monarch of a principality, as the heir to a royal throne, or as a male member of the immediate royal family. In its extended use princely often carries a strong implication of sumptuousness or of opulence or munificence.