Felt remorseful about (4)
I believe the answer is:
rued
'felt remorseful about' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rued that I've seen before include "Was sorry" , "was remorseful" , "'Regretted, repented (4)'" , "Was contrite about" , "Bitterly regretted" .)