Unbeknown a. : Not known; unknown.

Example:
Unbeknown to me my mom fed me salsa that contained beer, does my sobriety go out the window?

Taxonomy
unbeknownst, Merriam-Webster Online Dictionary, Dictionary, webster, english, Word Games, Webster Online Dictionary with audio pronunciations, thesaurus, Google Search, Custom Search, glossary, language, ESL, Search, knownst, adjective, Etymology, happening.

Defination from the web:
... Etymology: 1un- + obsolete English beknown known; unbeknownst, irregular from unbeknown. Date: 1636 ...