Magnificent devoted leader changing sides (5)

I believe the answer is:

royal

I'm a little stuck... Click here to teach me more about this clue!

'magnificent' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for royal that I've seen before include "As kings and queens" , "Kingly or queenly" , "King, queen, prince or princess?" , "- - Shakespeare Company (RSC)" , "Sail" .)

I've seen this clue in The Guardian.

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