unbeknown
From Longman Dictionary of Contemporary Englishunbeknownun‧be‧known /ˌʌnbɪˈnəʊn $ -ˈnoʊn/ (also unbeknownst /-ˈnəʊnst $ -ˈnoʊnst/ written) adverb [sentence adverb] → unbeknown to somebodyExamples from the Corpusunbeknown• But unbeknown to Ivor, Stroud had no intention of parting with the money.• You've crept back unbeknown to me.• Thus unbeknown to the competitors, the last valid part of the competition was removed four days before the submission date.• Under the old system many women amass secret savings unbeknown to their husbands.