which major series is this episode part of?
"The Office"
The Duel (The Office)
"The Duel" is the twelfth episode of the fifth season of the American comedy television series "The Office", and the show's 84th overall episode. 
when does andy find out angela is cheating In the episode "The Duel".
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The Duel (The Office) [SEP] Introduction
"The Duel" is the twelfth episode of the fifth season of the American comedy television series "The Office", and the show's 84th overall episode. In the episode, Andy learns his fiancee Angela is having an affair with Dwight, and the two challenge each other to a physical fight to win her affections. Meanwhile, Michael travels to New York City for a meeting with David Wallace, where Wallace seeks managerial advice from Michael due to the poor financial condition of the fictional company, Dunder Mifflin. The episode was written by Jennifer Celotta and directed by Dean Holland, the show's long-time editor making his directorial debut.