From Longman Dictionary of Contemporary Englishregretfullyre‧gret‧ful‧ly /rɪˈɡretfəli/ adverb 1 REGRET/FEEL SORRYfeeling sad because you do not want to do what you are doing ‘I must go, ’ he said regretfully.2 [sentence adverb]REGRET/FEEL SORRY formal used to talk about a situation that you wish was different or that you are sorry about SYN regrettably Regretfully, we do not have time to continue this discussion now.
Examples from the Corpus
regretfully• When the Muni stopped at Masonic I got off, regretfully.• "We'd better go back, " she said regretfully, "before it rains."• Because of our comparative approach, we must regretfully bypass interesting problems within the individual countries.• But also that day he sent a note to the Nawab, regretfully declining the invitation. 28 February.• Regretfully, Elliot was forced to close the business.• No, regretfully Mrs Field died before it could be arranged.• In the end he sent it, regretfully, to Paul, thus adding to the latter's troubles. 