How to reply soon, albeit curtly (7)

I believe the answer is:

shortly

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'curtly' is the definition.
('shortly' can be a synonym of 'curtly')

I don't understand the rest of the clue.

(Other definitions for shortly that I've seen before include "Soon; sharply" , "In a jiffy" , "Soon: in an abbreviated manner" .)

I've seen this clue in the Evening Standard.

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