After moral offence, monarch is collapsing (7)
I believe the answer is:
sinking
'is collapsing' is the definition.
(thesaurus)
'after moral offence monarch' is the wordplay.
'after' means one lot of letters go next to another.
'moral offence' becomes 'sin' (I've seen this before).
'monarch' becomes 'king' (king is a kind of monarch).
'sin' next to 'king' is 'SINKING'.
(Other definitions for sinking that I've seen before include "Going down" , "failing" , "Falling to the bottom" , "Declining" , "in decline" .)