Tyrannical ruler found in previous answer, after all (4)

I believe the answer is:

ivan

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'tyrannical ruler' is the definition.
The definition suggests a singular noun which matches the answer.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for ivan that I've seen before include "- - the Terrible (Czar)" , "Russian tsar called 'the Terrible'" , "in Russian history" , "man who had a terrible reputation" , "Tsar - 197> the Terrible" .)

I've seen this clue in The Guardian.

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