A doubter, but not one initially coming clean (7)

I believe the answer is:

aseptic

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

I don't understand how the remainder of the clue works.

(Other definitions for aseptic that I've seen before include "Paciest (anag.)" , "Free from bacteria, surgically clean" , "Sterile" , "avoiding germs" , "Free from harmful bacteria" .)

I've seen this clue in The Times.

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