Alan's note is startling in a way (11)

I believe the answer is:

sensational

I'm a little stuck... Click here to teach me more about this clue!

'startling in a way' is the definition.
I can't judge whether this defines the answer.

'alan's note is' is the wordplay.
'alan's note is' can be anagrammed to 'SENSATIONAL'.
Though, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for sensational that I've seen before include "Thrilling" , "Excellent" , "Mind-blowing" , "Spectacular" , "Very impressive" .)

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

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