As children, we are told to wish on a shooting star though unbeknownst to us the "star" was just a bit of space debris.
Some types of cat diseases are spread accidentally in catteries, unbeknownst to cat breeders.
Yet unbeknownst to her (or the reader), Aragorn has already pledged himself to Arwen, Elrond's daughter, a half-elven lady as far above him in station as he is above Eowyn.
Unbeknownst to either of them, a killer had dropped a highly lethal addition into Harriet's cold drink.
Unbeknownst to Jean, Mathew Knowles - Beyonce's father and now former manager - heard the song and decided he wanted it for his daughter.