The Man with Two Brians
Family Guy Season 7 Episode 5 (11/09/08)
When Brian gets injured during a take of Peter's version of Jackass the Griffins realize that Brian may be getting too old so Peter brings home a new dog prompting Brian to leave. Everyone else however loves "New Brian"; all except for Stewie, who does not like his constant happy attitude. Stewie kills "New Brian" and "Old Brian" returns and everyone doesn't seem to mind or even care.