Royal adjectives are listed in this post. Each word below can often be found in front of the noun royal in the same sentence. This reference page can help answer the question what are some adjectives commonly used for describing ROYAL.
ancient, astronomer, battle, british, e, entire
famous, few, first, former, front, great
her, his, last, late, main, many
most, new, old, other, own, port
prerogative, present, princess, recent, right, same
second, several, whole
Hope this word list had the adjective used with royal you were looking for. Additional describing words / adjectives that describe / adjectives of various nouns can be found in the other pages on this website.
Please add more adjectives to make this list more complete: