What bad plan needs to do with emaciated monarch (10)

I believe the answer is:

rethinking

'what bad plan needs' is the definition.
(a bad plan needs to be rethought)

'to do with emaciated monarch' is the wordplay.
'to do with' becomes 're' (regarding).
'emaciated' becomes 'thin' (similar in meaning).
'monarch' becomes 'king' (king is a kind of monarch).
're'+'thin'+'king'='RETHINKING'

I've seen this clue in The Times.

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