Revealed a secret about (5)
I believe the answer is:
outed
'revealed a secret about' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for outed that I've seen before include "Exposed against one's will" , "Revealed the homosexuality of (someone)" , "Revealed (someone) as gay" , "Exposed in public" .)