Revealed foul den destroyed by daughter (8)
I believe the answer is:
unfolded
'revealed' is the definition.
(unfolding is a kind of revealing)
'foul den destroyed by daughter' is the wordplay.
'destroyed' indicates anagramming the letters.
'by' says to put letters next to each other.
'daughter' becomes 'd'.
'foul'+'den'='foulden'
'foulden' anagrammed gives 'unfolde'.
'unfolde'+'d'='UNFOLDED'
(Other definitions for unfolded that I've seen before include "developed" , "Revealed; spread out" .)