King at this time, one unbelievable person not really so clever? (4-2-3)
I believe the answer is:
know-it-all
'person not really so clever?' is the definition.
(someone who acts like they know everything)
'king at this time one unbelievable' is the wordplay.
'king' becomes 'K' (abbreviation for king in chess).
'at this time' becomes 'now' (at the present time).
'one' becomes 'i' (Roman numeral).
'unbelievable' becomes 'tall' (e.g. 'a tall story').
'k'+'now'+'i'+'tall'='KNOW-IT-ALL'
(Other definitions for know-it-all that I've seen before include "Unteachable bigot" , "Smart alec" .)