lamentablemente
/lamenˌtableˈmente/ · B2 · adv
unfortunately, regrettably, sadly, woefully, regretfully, unluckily, lamentably, alas, disappointingly, tragically
lamentable + -mente (the Spanish -ly) = lamentably
Comes from Latin lamentari, to wail or mourn, which also gave English lament. Spanish forms adverbs with -mente, much like English uses -ly, so lamentable-mente maps neatly onto lament-ably.