unbeknown, unbeknownst -- ((usually used with `to') occurring or existing without the knowledge of; "a crisis unbeknown to me"; "she had been ill for months, unbeknownst to the family")
Overview of adv unbeknown
The adv unbeknown has 1 sense
unbeknown, unbeknownst -- (without someone's knowledge; "unbeknownst to me, she made all the arrangements")