Not entirely sane Roman? (4)

I believe the answer is:

nero

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'not entirely sane roman?' is the definition.
'Nero' can be an answer for 'roman?' (Nero was a Roman emperor). I am not certain of the 'not entirely sane' bit.

'not entirely sane roman?' is the wordplay.
'not entirely' says the answer is hidden in the clue.
'NERO' can be found hidden inside 'sane roman'.

Can you help me to learn more?

(Other definitions for nero that I've seen before include "Roman Emperor notorious for vice and luxury" , "Roman emperor on the fiddle?" , "Emperor, 'burnt' Rome" , "He's reported to have fiddled while Rome burned" , "Wicked fiddler" .)

I've seen this clue in The Times.

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