When it comes to Friends, fans of the show have spent years scrutinising every small detail of every episode to find mistakes and little moments they'd never noticed before.
Many of these have gone viral, as fans spotted actresses seemingly changing places during scenes, stars being replaced by body doubles and filming equipment accidentally cropping up in shots.
And now it seems there's another little blunder that eagle-eyed fans have spotted, all to do with a guest star from season 8 of the show.
In a post on the How You Doin forum on Reddit, a viewer shared a look at a still from season four, episode 9, The One Where They're Going To Party.
The image shows a newsstand on the street filled with magazines and on the cover of one is Hollywood star Brad Pitt.
Pitt is known by Friends fans for his appearance in the season 8 episode The One with the Rumour.
His role on the show was as Will Colbert, a broker, who went to high school with Ross and Monica and started an I hate Rachel club, before initiating a cruel rumour about Jennifer Aniston's character.
Fans who spotted his image on the magazine cover thought it was awkward that he was seen in the show before his character had been introduced.
Writing on Reddit, they said: "Brad Pitt spotted in a magazine before his cameo as broker 'Will Colbert'".
Other fans were quick to point out that this wasn't the only time an actor had been referenced or seen on the show, before they made a guest appearance.
In the comments, one person said: "So both Brad Pitt and Bruce Willis (the guys talk about how much they love Die Hard) both canonically exist in the Friends universe, but the characters never acknowledge Will nor Elizabeth's dad as their celebrity lookalikes."
Another said: "Same with Winona Ryder!"
A third joked that they were just "doppelgängers", adding: "They look like said celebrities but they're their own people!"
While a different user was just in awe that someone noticed in the first place, praising the poster for their "good eyes".
Did you spot this? Let us know in the comments below.
