Shakespearean king determined Christmas must be overturned (7)

I believe the answer is:

leontes

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'shakespearean king' is the definition.
The definition suggests a singular noun which matches the answer.

'determined christmas must be overturned' is the wordplay.
'determined' becomes 'set' (synonyms).
'christmas' becomes 'Noel' (Noel can mean Christmas).
'must be overturned' says the letters should be written backwards.
'set'+'noel'='setnoel'
'setnoel' reversed gives 'LEONTES'.

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I've seen this clue in The Independent.

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