Regretted (4)
I believe the answer is:
rued
'regretted' is the definition.
('rue' can be a synonym of 'regret')
This is all the clue.
(Other definitions for rued that I've seen before include "'Regretted, repented (4)'" , "was remorseful" , "Was contrite about" , "Bitterly regretted" , "Was sorry" .)