Control assumed by princeling ultimately? (5)

I believe the answer is:

reign

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'control' is the definition.
(I know that reign is a type of dominion)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for reign that I've seen before include "Rule over in Niger" , "Dominion" , "Sovereign's rule" , "Hold sway, rule" , "time in power" .)

I've seen this clue in The Independent.

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