mysteriously
adv. manneradv. in a way that is strange and difficult to explain. You use this when something happens and you do not know why or how it happened.
adv. in a manner that is difficult or impossible to understand, explain, or identify. Often used to describe events that seem to lack a logical cause.
The lights in the old house mysteriously turned on.
The ancient documents mysteriously disappeared from the locked safe overnight without any sign of a break-in.
The species, which had thrived for centuries in the isolated valley, mysteriously vanished from the fossil record long before the arrival of human settlers.
From Middle English misteriusly, equivalent to mysterious + -ly.
Typically placed after the verb or at the end of the clause to describe the nature of an action.