Friend supporting memorial in tremendous fashion (12)

I believe the answer is:

monumentally

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'friend supporting memorial in tremendous fashion' is the definition.
I can't tell whether this definition defines the answer.

'friend supporting memorial' is the wordplay.
'friend' becomes 'ally' (an ally is a friend or supporter).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'memorial' becomes 'monument' (synonyms).
'ally' after 'monument' is 'MONUMENTALLY'.

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I've seen this clue in The Times.

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