Unluckily

Some old men, by continually praising the time of their youth, would almost persuade us that there were no fools in those days; but unluckily they are left themselves for examples.

Source: tatoeba (411995)

The day promised to be a very gay and happy one, but— Unluckily, in a marionette's life there's always a "but" which is apt to spoil everything.

Source: tatoeba (2732945)

They say that Ngoc hoang sent a messenger from heaven to men to say that when they reached old age they should change their skins and live for ever, but that when serpents grew old they must die. The messenger came down to earth and said, rightly enough, "When man is old he shall cast his skin; but when serpents are old they shall die and be laid in coffins." So far so good. But unluckily there happened to be a brood of serpents within hearing, and when they learned the doom pronounced on their kind, they fell into a fury and said to the messenger, "You must say it over again and just the contrary, or we will bite you."

Source: wiktionary

[…] where Hercules and Omphale having changed garments, he lying in his wives clothes, and ſhe in his Lions skin, made the luſtfull God mistake ſo unluckily, […]

Source: wiktionary