After a gag is not funny anymore (6,1,4)

I believe the answer is:

beyond a joke

'not funny anymore' is the definition.

'after a gag' is the wordplay.
'after' becomes 'beyond'.
'gag' becomes 'joke' (I've seen this before).
'beyond'+'a'+'joke'='BEYOND A JOKE'

'is' is the link.

(Another definition for beyond a joke that I've seen is " Past being funny".)

I've seen this clue in The Mirror.

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