Cast of TV show "Friends" in 1996. Photo / Supplied
One of the world's most famous actors freaked out while filming a guest spot on Friends in the '90s.
Charlie Sheen played Phoebe's old flame, Ryan, in a season two episode called The One With The Chicken Pox.
But according to Saul Austerlitz, author of the book Generation Friends, Sheen struggled to cope with working in front of a studio audience.
"In a way, making a television series, especially one that's shot on a soundstage, is a little bit like doing theatre," Austerlitz said. "You're in front of an audience, the audience is watching you, you're doing things in real time.
"Charlie Sheen at the time was a movie star. He just wasn't used to having an audience of people watching what he was doing.
"The director of the episode that Charlie Sheen was in noticed after a while that his legs were basically knocking together as he was performing. He was so nervous at the thought of this audience that he wasn't able to settle," Austerlitz told news.com.au.
The director temporarily halted filming and summoned Sheen's brother, Emilio Estevez, who was watching from the sidelines.
"[Emilio] calmed him down and talked him through it so he could perform his role to the best of his ability," Austerlitz said.
In Generation Friends, Austerlitz also explains why Friends travelled to London to film an episode, and which billionaire negotiated a cameo appearance in the episode.
"It was essentially a business decision," the author said about the season four episode, The One With Ross's Wedding.
"This was right around the time that DVD box sets started to be a major source of revenue. Kevin Bright, who was the financial mastermind of Friends and one of the show's creators, realised that the UK sales for Friends box sets were enormous and he started thinking about ways that they could pay tribute to the British fans and acknowledge them."
He pitched to NBC that they film an episode in London, but the network initially baulked given the huge cost of flying the entire cast and crew overseas.
Enter Sir Richard Branson.
"They ended up being put in touch with Richard Branson and he offered them a deal where he would fly over everybody on his airline," Austerlitz told news.com.au.
But there was a catch.
"What he asked for in return was that he have a cameo on the show," the author said.
The show's creators agreed to the deal but were less than impressed with Branson's acting skills.
"The sense was that he was not a naturally born actor necessarily … but sort of managed to crawl across the finish line," Austerlitz laughed.
There was meant to be a character called 'Pat the Cop'
In his book, Austerlitz reveals there was meant to be a character on the sitcom nicknamed 'Pat the Cop'.
The character came about because NBC bosses were worried audiences wouldn't be interested in a show all about a group of 20-somethings.
"They [NBC] got a little bit spooked and thought, 'We have this show about six people in their 20s, what is an older audience going to latch on to?' " Austerlitz told news.com.au.
"They were really insistent on this idea that they have some sort of older character who's going to be a father figure type and they strongly suggested to David Crane and Marta Kauffman, the creators of the show, that they introduce a character along those lines.
"Amongst Crane and Kauffman and the writers of this show, they ended up calling this character in their minds 'Pat the Cop' named after a fatherly figure that some of the writers had known when they were college students."
The creators and the writers hated the idea though, and came up with a clever plan to ensure the character of 'Pat the Cop' never made it into the show.
"They decided to tank it and to write it as poorly as they could," Austerlitz said.
And the plan worked.
"Once NBC saw what it was going to be like they pulled back and said, 'You know what, we're good with the six characters you've got,' " Austerlitz said.