A senior Byzantine court title that was bestowed on the sons or sons-in-law of reigning emperors (6)

I believe the answer is:

despot

(Other definitions for despot that I've seen before include "One exploiting rule" , "Arbitrary ruler" , "Possibly 4 [CZAR]" , "Tyranical dictator" , "who treats others badly?" .)

I've seen this clue in The Independent.

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