One badly behaved fan, ten, conceivably (6,8)

I believe the answer is:

enfant terrible

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'one' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'badly behaved fan ten conceivably' is the wordplay.
'badly behaved' is an anagram indicator.
'conceivably' becomes 'terrible' (I can't explain this - if you can you should give a lot more credence to this answer).
'fan'+'ten'='fanten'
'fanten' anagrammed gives 'enfant'.
'enfant'+'terrible'='ENFANT TERRIBLE'

Can you help me to learn more?

(Other definitions for enfant terrible that I've seen before include "Difficult issue in France" , "subject of controversy? - with 10a" , "wild child - with 30a" , "nonconformist" , "scamp" .)

I've seen this clue in The Telegraph.

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