Chandler then enters and Phoebe begins flirting with him.
Chandler and Monica have known each other since they were in their late teens.
In Central Perk, Rachel and Phoebe tell Joey that Phoebe has found out about Monica and Chandler.
Joey is relieved that enough people know that they can finally confront their friends about their relationship, but Phoebe and Rachel decide to mess with them instead, for fun.
Just imagine all of the hilarity we would have missed out on if it had ended after London!
As Friends wrapped up its fourth season in May of 1998, Ross and Rachel's on/off relationship still provided the show's emotional core, with the other four roommates serving as the platonic Greek chorus to the couple's climactic kisses and "on-a-break"-dom.
And the scene where Chandler and Phoebe are finally facing each other in their seduction battle is awesome.
While Rachel, Ross and Phoebe are having a look around the apartment, Phoebe looks through the window into Monica's Apartment, and sees Monica and Chandler having sex.
When Phoebe finds out about the Monica/Chandler affair, she tests Chandler via flirtation.
Ugly Naked Guy's apartment goes up for rent and Ross wants it.
If we're ever looking for another relationship, that's something to file away.'" The notion of Monica and Chandler was also seriously pitched in the writers' room in season three, Silveri says.
"The One Where Everybody Finds Out" (also known as "The One Where Phoebe and Ross find out") is the fourteenth episode of the fifth season of Friends, which aired on February 11, 1999.