Devotee mostly liking everything in Frozen tremendously (13)

I believe the answer is:

fantastically

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'tremendously' is the definition.
Both the answer and definition are adverbs. Perhaps there's a link between them I don't understand?

'devotee mostly liking everything in frozen' is the wordplay.
I cannot quite see how this works, but
'devotee' could be 'fan' (synonyms) and 'fan' is present in the answer.
'everything' could be 'all' (all things) and 'all' is present in the answer.
'frozen' could be 'icy' (similar in meaning) and 'icy' is found in the remaining letters.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Times.

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