HAVEN'T I cryptically written Russian tsar? (4,3,8)

I believe the answer is:

ivan the terrible

I'm a little stuck... Click here to teach me more about this clue!

'russian tsar?' is the definition.
(I've seen this before)

'haven't i cryptically written' is the wordplay.
'cryptically' indicates an anagram.
'written' becomes 'terrible' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'havent'+'i'='haventi'
'haventi' is an anagram of 'ivanthe'.
'ivanthe'+'terrible'='IVAN THE TERRIBLE'

Can you help me to learn more?

(Other definitions for ivan the terrible that I've seen before include "despot" , "Cruel tyrant" , "Dictator" , "dismissive review of Denisovich film?" , "Russian leader's" .)

I've seen this clue in the Sydney Morning Herald.

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