Cheese with a fly on, just for the moment (4)

I believe the answer is:

brie

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'cheese' is the definition.
(I know that Brie is a cheese)

I can't explain the rest of the clue.

(Other definitions for brie that I've seen before include "cheesy stuff" , "cheese-producing region" , "Prov. squalid place" , "Round soft Fr. cheese" , "Variety of cheese" .)

I've seen this clue in the Evening Standard.

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