Query: By what season was American Idol the most watched show on TV?
Context: By season three, the show had become the top show in the 18–49 demographic a position it has held for all subsequent years up to and including season ten, and its competition stages ranked first in the nationwide overall ratings. By season four, American Idol had become the most watched series amongst all viewers on American TV for the first time, with an average viewership of 26.8 million. The show reached its peak in season five with numbers averaging 30.6 million per episode, and season five remains the highest-rated season of the series.