The story
- Proto-Italic*wre-
- Latinre-
- Old Frenchre-
- Proto-Indo-European*ǵʰreh₁d-
- Proto-Germanic*grētaną
- Frankish*grātan
- Old French*greter
- Old Frenchregreter
- Middle Englishregretten
- Englishregretting
- English todayregrettingly
From regretting + -ly.
Etymology from Wiktionary, CC BY-SA 4.0.