Relief after agent returned (6)
I believe the answer is:
repaid
'returned' is the definition.
('repay' can be a synonym of 'return')
'relief after agent' is the wordplay.
'relief' becomes 'aid' (I've seen this before).
'after' is a charade indicator (letters next to each other).
'agent' becomes 'rep' (short for representative).
'aid' put after 'rep' is 'REPAID'.
(Other definitions for repaid that I've seen before include "no longer outstanding" , "Recompensed" , "Refunded or rewarded" , "Diaper (anag.)" , "Reimbursed" .)