A blunder borne out! (5)

I believe the answer is:

boner

'a blunder' is the definition.
('boner' can be a synonym of 'blunder')

'borne out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'borne' anagrammed gives 'BONER'.

(Other definitions for boner that I've seen before include "Stupid mistake" , "butcher?" .)

I've seen this clue in the Evening Standard.

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