Warning for Harry Potter to stop illusion ultimately (7)

I believe the answer is:

portent

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'warning' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for portent that I've seen before include "bad sign" , "Sign of thing to come" , "Warning of momentous event" , "Evil omen" , "Augury" .)

I've seen this clue in The Hindu.

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