Friend given a portion of fish in the end (4)

I believe the answer is:

ally

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'friend' is the definition.
(an ally is a friend or supporter)

I don't understand how the rest of the clue works.

(Other definitions for ally that I've seen before include "Friendly nation" , "Friend in time of need" , "Join - friend" , "State formally cooperating with another" , "One co-operating with another" .)

I've seen this clue in the Evening Standard.

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