Defeated king flees, revealed as gay? (5)
I believe the answer is:
outed
'revealed as gay?' is the definition.
'defeated king flees' is the wordplay.
'defeated' becomes 'routed' (routing is a kind of defeating).
'king' becomes 'r' (r is abbreviation for rex).
'flees' is a deletion indicator.
'routed' with 'r' taken out is 'OUTED'.
(Other definitions for outed that I've seen before include "Exposed in public" , "Revealed the homosexuality of (someone)" , "Exposed against one's will" , "Revealed (someone) as gay" .)