unbeknown to somebody
From Longman Dictionary of Contemporary Englishunbeknown to somebodyunbeknown to somebodyNOT KNOWwithout that person knowing about it Unbeknown to him, his wife had been trying to phone him all morning. → unbeknownExamples from the Corpusunbeknown to somebody• Unbeknownst to the public, he was involved in covering up the scandal that was to rock the nation.• Unbeknown to me, Denise had her own plan.