An adverb meaning 'unfortunately' or 'unluckily'; used in both spoken and written Japanese and can carry a note of sympathy.
不幸にも彼はその日事故に遭ってしまった。
Unfortunately, he was involved in an accident that day.
不幸にも財布を落としてしまい、身分証も一緒になくなった。
Unluckily, I lost my wallet and my ID was inside it.
不幸にもその日は雨で、ピクニックは中止になった。
Unfortunately, it rained that day and the picnic was cancelled.