Regretfully Use the adverb regretfully to mean "with regret" — the sorrow you feel about something that has already happened. For example, little kids would regretfully turn over the candy bars they stole from the grocery store. Regrettably The sentence adverb regrettably is good for expressing regret, or sorrow, about an unfortunate event. If you forgot that today, May 5th, is your brother's birthday, you might say, "Regrettably, I thought today was the fourth." [Source](https://www.vocabulary.com/articles/chooseyourwords/regrettably-regretfully/)