Chum (boy) one accompanying a knight in classical style (9)

I believe the answer is:

palladian

'in classical style' is the definition.

'chum boy one accompanying a knight' is the wordplay.
'chum' becomes 'pal' (both can mean a friend).
'boy' becomes 'lad' (informal term for boy).
'one' becomes 'i' (Roman numeral).
'accompanying' says to put letters next to each other.
'knight' becomes 'n' (chess abbreviation).
'pal'+'lad'+'i'+'a'+'n'='PALLADIAN'

(Another definition for palladian that I've seen is " Neoclassical architectural style".)

I've seen this clue in The Guardian.

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