The production of this series caused tension on the set of Three's Company (1976) between John Ritter and the rest of the cast. The producers tried to keep it a secret from the rest of the cast. But they eventually found out and were disappointed that the series would essentially continue without them.
Coincidentally, Jessica Walter had starred in a TV movie also called Three's a Crowd (1969). However, that movie was about an airline pilot who was a bigamist, having two families in two different cities.