in self-defense occurs where a person,
without any fault on his part in provoking or bringing on the
difficulty, kills another under reasonable apprehension of
death or great bodily harm to himself. . . .
in self-defense occurs where the accused,
although in some fault in the first instance in provoking or
bringing on the difficulty, when attacked retreats as far as
possible, announces his desire for peace, and kills his
adversary from a reasonably apparent necessity to preserve his
own life or save himself from great bodily harm.
Bailey v. Commonwealth, 200 Va. 92, 96, 104 S.E.2d 28, ___ (1958).