Briefly assist veteran stalked by two Celts in central Europe (8)

I believe the answer is:

helvetii

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'celts in central europe' is the definition.
The definition suggests a plural noun which matches the answer.

'briefly assist veteran stalked by two' is the wordplay.
'briefly' means to remove the last letter.
'assist' becomes 'help' (synonyms).
'veteran' becomes 'vet' (abbreviation).
'stalked by two' becomes 'ii' (I am not sure about this - if you are sure you should believe this answer much more).
'help' with its last letter taken away is 'hel'.
'hel'+'vet'+'ii'='HELVETII'

Can you help me to learn more?

(Another definition for helvetii that I've seen is " Celtic tribe".)

I've seen this clue in The Independent.

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