un·be·known 
(ŭn′bĭ-nōn)
(ŭn′bĭ-nōn)adj.
Occurring or existing without being known; unknown: a crisis unbeknown to us.
[UN-1 + obsolete beknown, known (from Middle English beknowen, past participle of beknowen, to get to know, from Old English becnāwan : be-, be- + cnāwan, to know; see KNOW).]