Relationship with Candace Flynn and Stacy Hirano
Billy is never seen in the series, and mentioned only once.
It is possible that Billy had to leave Danville sometime later the third grade, or he still lives there somewhere, but never talks to Candace or Stacy.
It is also possible that Billy would be living in Danville, but never seen. However, this is not likely to have been happened since Candace and Stacy would have been still flirting with him. It is also possible that he is living in Danville but Candace and Stacy are not flirting because they have found Jeremy and Coltrane.
- "Spa Day" (Mentioned only)