Talk about seeing double!
The gimmick to The Patty Duke Show had the star playing identical cousins. Cathy Lane (Duke) emigrated to the US from Scotland to live with her cousin, Patty (Duke again) and her family. If you thought that was enough "twin magic", think again. In one second season episode, Duke played a 3rd Lane cousin and gained special guest star credit, something that wouldn't happen today.
In addition, the cousins' dads were played by the same actor as well, nattily dressed William Schallert, who played Martin Lane's twin brother in 3 season 1 episodes, and added a 3rd persona in the form of an uncle, Jed, later in the series.
Maybe it should surprise no one that the concept was the work of two men who would utilize the "twin magic" gimmick after moving to Screen Gems the next year. William Asher created Bewitched, and eventually went with the identical cousin gimmick. Future best-selling author Sidney Sheldon followed that with I Dream of Jeannie, which bowed during Duke's final season (1965), but opted for the standard twin sister instead of cousin for star Barbara Eden. Jeannie, of course, aired on NBC, while Bewitched and Duke aired on ABC. Y'think maybe the folks at United Artists, which produced Duke, rued the day they let Sheldon & Asher jump to Screen Gems?
Currently, This TV, which has a lot of MGM/Sony properties on its roster, airs Duke. Check local listings. In the meantime, scope out the open:
Schallert was later used as a studio announcer at ABC for a few years before ceding the gig to Ernie Anderson. Duke parlayed the sitcom into a brief singing career, leading to a crossover with Shindig!.