One car addict will be upset by it (4,8)

I believe the answer is:

road accident

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'be upset by it' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'one car addict' is the wordplay.
'one car addict' anagrams to 'ROAD ACCIDENT'.
But, I am not clear how the anagram is indicated.

'will' is the link.

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I've seen this clue in The Globe and Mail.

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