I was not aware of this

unawares /  ên-ê-werz /  adverb

1. Without thinking, without being aware, inadvertently, unconsciously.  
2. By surprise, suddenly and without warning. We are generally caught unawares by unusual things.

Dr. Goodword: This word is an oddity: the adverb for unaware is formed by adding the ubiquitous suffix -s: unawares. This is so unusual, most dictionaries are now disposed to accept mundane unawarely as an option.

History: Unawares is a lexical palimpsest. If we remove the final -s, we are left with unaware, the negative of aware, which means "conscious, vigilant". Aware itself is an 'adjective-adverb' that occurs only in the predicate: "The lady was aware of . . ." but not "the aware lady". Most such words carry the prefix a-, e.g. afloat, asleep, aloft, as does aware. Remove that prefix and we come to a noun ware "alert, on guard" that hasn't been used for 500 years, even though its adjective, wary, is still around. We also find it in beware, which was originally two words: be ware, in the sense of "be wary".