Theologian, ’e's wearing a red top? That's unexpected (6)

I believe the answer is:

sudden

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'unexpected' is the definition.
(similar in meaning)

'theologian 'e's wearing a red top?' is the wordplay.
'theologian' becomes 'dd' (Doctor of Divinity degree).
'wearing' is an insertion indicator.
'a red top?' becomes 'sun' (I can't justify this - if you can you should give a lot more credence to this answer).
'dd'+'e'='dde'
'dde' placed inside 'sun' is 'SUDDEN'.

'that's' acts as a link.

Can you help me to learn more?

(Other definitions for sudden that I've seen before include "'Unexpectedly, without warning (6)'" , "Quickly, without notice or warning" , "Swift" , "Quick and unexpected" , "Done unexpectedly" .)

I've seen this clue in The Guardian.

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