"The One Where They Leave In Rachel's Stand-In" might not be an actual Friends episode, but it did happen. Twice.

Almost 20 years after the show went off air, the beloved sitcom has once again gone viral after fans spotted a major editing mistake. In season 9, episode 15 of the show titled "The One With The Mugging," there is a scene where the camera pans to Joey, played by Matt LeBlanc, with what is supposed to be Jennifer Aniston's Rachel standing in the background. Except it's not Jennifer Aniston. It's her stand-in—and half of her face just visible past Joey. 

And on top of that, it turns out this isn't the only time this exact mistake was made during the same season. 

In the fourth episode of season nine, "The One With The Sharks," Jennifer's stand-in once again makes it into the final cut. Caught by a fan and then shared to Twitter, approximately 12 and a half minutes into the episode, a curly-haired Rachel can be seen at the kitchen table wearing a yellow shirt. When the camera shifts to the table again, Jennifer's straight-haired stand-in has taken her place wearing a blue shirt.

Mistakes aside, Friends' popularity has endured since it ended nearly 20 years ago. And while it may not be joining its fellow sitcoms Will & Grace and Saved by the Bell  in seeing a revival, the cast did come together in 2021 for a reunion special.

Friends: The Reunion was an emotional experience for fans and cast alike, with former cast mates Jennifer, Matt, Courtney Cox, Lisa Kudrow, Matthew Perry, and David Schwimmer walking together down memory lane. But amid the good times, Jennifer was caught off guard by some of the harder emotions that came up while filming the special. 

"In your mind you think, 'Oh, this will be really fun to time travel,'" she told Rob Lowe on his podcast Literally! with Rob Lowe in September 2021. "It turns out, ooh, ouch, it's kind of hard to time travel."

As she continued, Jennifer highlighted how surreal it was to see the set, which had "the exact same everything, down to the little tchotchkes on the shelves." But while the set remained the same, Jennifer knew that she and her co-stars had not. 

"You know, [in] 16 years, a lot has gone on for each of us," she continued. "And 16 years ago, we were all sort of wide-eyed and bushy-tailed, and sort of had our whole lives ahead of us—even though we were heartbroken to say goodbye to these 10 years and this family and these people and the job we all loved to do."

For the latest breaking news updates, click here to download the E! News App