The feud started with Vivian over resentment over Frawley’s age
Vivian Vance saw herself as a more glamorous and, perhaps understandably, more youthful character than Ethel Mertz. She felt that Frawley’s Fred aged her, once commenting off-set that he should be playing her father, rather than her husband. Frawley somehow got wind of her comments, and they did not sit well. She made other disparaging remarks about her costar, included referring to him as a “stubborn little Irishman”. Their relationship offstage deteriorated to the point they seldom spoke to each other, which eventually spilled over into disputes during script readings and other meetings. Frawley began working with writers to add venom to his in-character remarks regarding Ethel’s appearance. They were tolerated because they got laughs, which for I Love Lucy came from a live audience during filming. According Desi Arnaz, writing in his autobiography A Book, Frawley disliked Vance from the beginning, and didn’t hesitate to say so.
The barbs between the Mertz’s became an integral part of the highly successful show, and none of the principals wanted to meddle with a successful recipe. According to Arnaz, Vance had triggered it, but beyond that it was Frawley who would not let it go. After I love Lucy ceased production Arnaz offered the pair their own show, featuring the Mertz’s in what would have been one of television’s early spin-offs. Frawley liked the idea; Vance would have none of it. Instead, she joined Lucille Ball’s new show, though not as Ethel, and he joined My Three Sons, where subsequent reports were that his drinking habits, kept in check on I Love Lucy, re-emerged. After Lucy they never worked together again, and Frawley once told an interviewer, of Vance, “She’s one of the nicest girls to ever come out of Kansas. I wish she’d go back there”.