flabbergastingly

Flabbergastingly is an adverb describing something done in a manner that causes extreme surprise or astonishment.

It intensifies whatever it modifies, suggesting the degree is almost beyond belief: The restaurant was flabbergastingly expensive.

Though built from the well-established verb flabbergast, this adverb form remains uncommon and carries a playful, emphatic quality suited to informal contexts where ordinary intensifiers like extremely or incredibly feel insufficient.