If you describe something as inconceivable, you think it is very unlikely to happen or be true. It was inconceivable to me that Toby could have been my attacker = unthinkable. too strange or unusual to be thought real or possible
Not conceivable; incapable of being conceived by the mind; not explicable by the human intellect, or by any known principles or agencies; incomprehensible; as, it is inconceivable to us how the will acts in producing muscular motion