My Sister, the Home Wrecker I Dream of Jeannie : Season 5 Episode 12

Jeannie's sister returns for a final time to foul things up again. This time, she poses as her sister and makes the others think she is having an affair with another astronaut named Biff Jellico (Played by Eden's real life husband Michael Ansara) all the while Tony and Jeannie are oblivious to it.