Revealed: Jennifer Aniston and Courteney Cox were secretly replaced on Friends - but no one noticed... until now

Eagle-eyed viewers recently noticed scenes of the hit show where doubles for Rachel (played by Aniston) and Monica (played by Cox) were used - and their unfamiliar faces made it into the aired episodes. The result is a jarring moment where two people who only have a slight resemblance to the actresses pop up on screen. Around three minutes into Episode 15 from Series Nine, Rachel disappears from the friends' New York City apartment and is replaced by a lookalike wearing a different shirt to the left of the screen (bottom left). In the Season 8 episode, 'The One With Rachel's Date,' Monica too is swapped with a woman with a completely different hairstyle sitting in the Central Perk coffee shop, having a conversation with Phoebe. The scenes were filmed in 2001 and the double trouble trickery was only discovered by fans recently.