Is it a bit of a surprise for a Frenchman to be imperturbable? (6)

I believe the answer is:

serene

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'be imperturbable?' is the definition.
(I've seen this in another clue)

I can't explain the remainder of the clue.

(Other definitions for serene that I've seen before include "Calm, untroubled" , "Calm and at peace" , "Peaceful and contented" , "Calm and relaxed" , "still" .)

I've seen this clue in the Evening Standard.

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