Old, cunning Byzantine governor (6)

I believe the answer is:

exarch

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'byzantine governor' is the definition.
'exarch' can be an answer for 'governor' (thesaurus). I am not certain of the 'byzantine' bit.

'old cunning' is the wordplay.
'old' becomes 'ex'.
'cunning' becomes 'arch' (I've seen this before).
'ex'+'arch'='EXARCH'

Can you help me to learn more?

(Another definition for exarch that I've seen is " Bishop".)

I've seen this clue in The Hindu.

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