How remarkable, a French horn! (3)

I believe the answer is:

cor

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'french horn' is the definition.
('horn' in French)

I don't understand the remainder of the clue.

(Other definitions for cor that I've seen before include "Gosh" , "Blimey" , "Expression of surprise" , "Surprised expression" .)

I've seen this clue in the Evening Standard.

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