Not entirely together, EU pontificates on this (8)

I believe the answer is:

hereupon

'on this' is the definition.

'not entirely together eu pontificates' is the wordplay.
'not entirely' indicates the answer is hidden within the clue.
'HEREUPON' can be found hidden inside 'together eu pontificates'.

(Another definition for hereupon that I've seen is " Immediately after this".)

I've seen this clue in The Times.

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