What if it's something to do with the mirror of fate? A dark mirror reflection of Trevor? I mean, the mirror is important somehow, right?
That way it can not be Trevor, (because it's Alucard" and also not be Trevor Becoming Alucard, since he doesnt it's a mirror image.
Im still thinking Trevor dies or something though.
Or Cox is lying to us because, well, hes not just gonna say OH YEAH TREVOR BECOMES ALUCARD because he wants to keep us guessing till we see first hand.