Certainly true, cunningly hiding medals (2,2,4)

I believe the answer is:

to be sure

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'certainly' is the definition.
(thesaurus)

I can't explain the remainder of the clue.

(Other definitions for to be sure that I've seen before include "Admittedly" , "Undoubtedly" , "Of course, certainly" , "I admit" , "Without doubt" .)

I've seen this clue in The Times.

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