Stunning success in Iona ruined Greek fellowship (8)

I believe the answer is:

koinonia

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'fellowship' is the definition.
(I know that koinonia is a type of fellowship)

'stunning success in iona ruined' is the wordplay.
'stunning success' becomes 'ko' (I can't justify this - if you can you should give a lot more credence to this answer).
'ruined' indicates anagramming the letters.
'iona' anagrammed gives 'onia'.
'ko'+'in'+'onia'='KOINONIA'

'greek' is the link.
I am not very happy about this link. It may belong to another bit of the clue.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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