"More royal" and "most royal". "This queen's voice sounds more royal than the previous queen's voice did."
If the word is 1 syllable, say -er and -est
bigger, smartest
If the word is 3 or more syllables, say "more" and "most"
More intelligent, most enthuiastic
If the word contains 2 syllables, look at the last letter.
If the last letter is "y", ier/iest and more/most are both acceptable, but ier/iest is preferred
uglier, happiest
If the word ends in any other letter, say more and most
more upset, most alive, most royal
EXCEPTION: more fun, not funner
EXCEPTION TO EXCEPTION: In parts of Canada, Australia, and the west coast of the US, it is OK to say "funner" in casual speech, but not in writing.