What Mr Stone becomes (7)

I believe the answer is:

monster

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'what mr stone becomes' is the definition.
I can't tell whether this defines the answer.

'mr stone becomes' is the wordplay.
'becomes' indicates anagramming the letters.
'mr'+'stone'='mrstone'
'mrstone' anagrammed gives 'MONSTER'.

Can you help me to learn more?

(Other definitions for monster that I've seen before include "Enormous or grotesque being" , "Gigantic" , "Fabled giant animal" , "Beast - on terms (anag)" , "Ugly and frightening beast as in 8 Across" .)

I've seen this clue in The Irish Independent.

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