Knackered after sex? (4,2)

I believe the answer is:

past it

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'knackered' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'after sex?' is the wordplay.
'after' becomes 'past' (I've seen this in other clues).
'sex?' becomes 'it' (a common euphemism).
'past'+'it'='PAST IT'

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(Other definitions for past it that I've seen before include "No longer competent" , "Ageing" , "Too old for anything" , "Far from fresh" , "No longer capable" .)

I've seen this clue in The Times.

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