Old king’s pronouncement after enlightenment by bishop (4)
I believe the answer is:
ahab
'old king's' is the definition.
(I've seen this before)
'pronouncement after enlightenment by bishop' is the wordplay.
'pronouncement after enlightenment' becomes 'aha' (you might say 'aha!' after understanding something).
'by' is a charade indicator (letters next to each other).
'bishop' becomes 'B' (chess abbreviation).
'aha'+'b'='AHAB'
(Other definitions for ahab that I've seen before include "one who hunted whales" , "Whaling Captain" , "Jezebel's husband, wicked king in the 'Old testament'" , "Jezebel's husband - Moby Dick's hunter" , "One whose nemesis was white" .)