"unbeknown" in the adjective sense
1. 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"
"unbeknown" in the adverb sense
1. unbeknown, unbeknownst
without someone's knowledge
"unbeknownst to me, she made all the arrangements"
Source: WordNet® (An amazing lexical database of English)
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