Treated to a parting observation (4,3)

I believe the answer is:

seen off

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'a parting observation' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'treated to' is the wordplay.
'treated' becomes 'seen' (I've seen this in another clue).
'to' becomes 'off' (I can't explain this - if you can you should give a lot more credence to this answer).
'seen'+'off'='SEEN OFF'

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I've seen this clue in the Evening Standard.

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