Set free knight who's regularly hidden assets (9)

I believe the answer is:

strengths

'assets' is the definition.
(strength is a kind of asset)

'set free knight who's regularly hidden' is the wordplay.
'regularly hidden' means one should take alternating letters.
'set'+'free'+'knight'+'whos'='setfreeknightwhos'
The alternating letters of 'setfreeknightwhos' are 'STRENGTHS'.

I've seen this clue in The Everyman puzzle in The Observer.

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