Here's the Real Reason Why William Frawley Was Replaced on My Three Sons

The series ran from 1960 to 1972 and followed widowed father Steve Douglas (Fred MacMurray) raising his three sons with help from extended family. It started on ABC in black-and-white and eventually moved to CBS in color, making it one of the longest-running sitcoms of its time.

But halfway through Season 5, something changed. Frawley, who had played Bub since the pilot, vanished from the show—replaced by William Demarest as Uncle Charley. And viewers were left wondering: what happened?

Turns out, the answer wasn't creative differences or backstage drama. It was insurance.

In the fall of 1964, Desilu Studios (which produced the show) declared William Frawley unfit to continue working due to his declining health. He was 77 at the time, and the studio had been informed that insuring him had become too expensive. Frawley continued filming through midseason while they looked for a replacement.

The studio solution: write Bub out of the show, send him "back to Ireland to visit Aunt Kate for her 104th birthday," and bring in his brother Charley—a gruff but lovable merchant sailor and amateur cellist played by Demarest—to take over the caregiving duties.

Frawley's health issues were serious enough that he officially left the show before the season ended. He passed away less than two years later, on March 3, 1966.

So while Bub's sudden disappearance was wrapped in a warm storyline, the real reason was simpler and far less sentimental:

• Frawley's age and medical condition made him difficult to insure
• Desilu Studios ruled him unfit to continue
• William Demarest was brought in as a safer, insurable replacement

The casting switch worked well enough for the show, which continued for another seven seasons. But for longtime fans, Bub's exit remains one of the earliest examples of a behind-the-scenes decision rewriting the script — not for drama, but for dollars.