Duncan Edward Harris (Mitchel Musso) is Nick's only childhood friend. He and Nick have been together since they were little kids. Therefore, Duncan has moved to New York City for Kindergarten. In Best Friends Forever: The Movie, Duncan went back to Los Angeles to met up with Nick to spent the time together at Disneyland, till he grabs Maria's hat and begins dating with her. But in an episode, "Is This The End", the final season of the third, it was revealed that he and Maria broke up. He returns in "How To Get Them Back Together" where he resumes his relationship with Maria. Duncan graduated from high school in the series finale but he and Maria are not together for college.