Joey's fake identical twin Carl, played by Louis Mandylor, almost played the real character in Friends did not age well, it remains ever-relevant with its fanbase only growing thanks to younger viewers who are discovering it through reruns and availability in streaming.
Despite the many great aspects of the show, however, its main draw was always the chemistry among the six main cast . Unlike many sitcoms, which focus on one or two main characters in a group of people while the rest are ing characters, Friends was a true ensemble. Each member of the Central Perk gang was given respective arcs and time under the spotlight. This carefree and light vibe that the sitcom exuded came from the natural dynamic of the actors. Jennifer Aniston, David Schwimmer, Courteney Cox, Lisa Kudrow, Matthew Perry, and Matt LeBlanc genuinely liked hanging around with each other and throughout Friends' run, they also became friends off-screen.
Given this, it's difficult to imagine anyone else playing the characters other than the actors who did. However, had things turned out differently, the main cast would've looked so much different. As revealed in the Friends: The One Where They Got Back Together reunion show, the producers had a few hurdles casting the roles. For example, Perry and Aniston were committed to other projects so they couldn't simply the NBC sitcom. Meanwhile, LeBlanc, who was struggling as an actor at that time much like his character, Joey, revealed in the Friends reunion he almost lost the role to another candidate. Luckily, he landed the gig, but his old competitor, Louis Mandylor, once made a guest appearance on the show. Mandylor's character, Carl, appeared in Friends season 6, episode 17 "The One With Unagi." Joey hired him to pretend to be his identical twin so they could enter a medical research program to earn some cash. Joey coached Carl to be more like him, oblivious to the fact that they look nothing like each other.
Carl only briefly appeared on the show, but if his Friends audition and casting had gone his way, Mandylor could've been the series regular who played Joey Tribbiani for 10 seasons. It must have been an odd feeling to be asked to come back to the show in a cameo role years later after it had become a massive hit. While it may have been a little uncomfortable for some to take the short stint on Friends, it didn't seem like there's any animosity from him since he gamely did the guesting appearance.
Luckily, it wasn't as though missing out on Friends killed his career. Mandylor has also appeared in My Big Fat Greek Wedding, Big Fat Greek Wedding 2, Matt LeBlanc. As previously mentioned, the cast's chemistry was a big reason why the sitcom became such a hit. Removing any one of them could've significantly changed the overall vibe of the series.