Incompetent monarch changing sides (5)

I believe the answer is:

clown

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'incompetent' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?

I don't understand how the rest of the clue works.

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(Other definitions for clown that I've seen before include "Joker" , "Buffoon" , "Jester" , "Red-nosed, long-shoed entertainer" , "Foolish chap" .)

I've seen this clue in The Times.

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