surely not; certainly not
Used with a negative sentence to express strong disbelief or conviction that something cannot happen. Often carries a rhetorical or emphatic tone.
よもや彼がそんなことをするとは思わなかった。
I never thought he would do such a thing.
よもや負けるとは思っていなかった。
I never dreamed we would lose.
Surely he can't be the culprit.
Surely he wouldn't say such a thing.
I never imagined he would actually win.