If this was soft resetting the starter, or Breeding without the Masuda Method your looking at a 1/8192 chance times a 1/8 chance, equalling to 1/65536.
If this was Masuda Breeding, your instead looking at 1/8 chance times a 1/1638 chance, equalling to 1/13104. Quite a lucky find regardless.
Hope I Helped.