regrettably
adv.in a way that makes you feel sorry or unhappy. You use this when you have to say something bad or when you are apologizing.
adv.in a manner that causes or expresses regret. Often used to introduce negative news or to soften the impact of an apology.
“Regrettably, we cannot accept your application this year.”
“The manager regrettably informed the team that the project would be cancelled due to a lack of funding.”
“Although the results were disappointing, the researchers regrettably concluded that the current data did not support their initial hypothesis regarding the new treatment's efficacy.”
“Jokes, a reliably dark pleasure in Cusk’s work, are in regrettably short supply.”
From regrettable + -ly.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.