Freddie Prinze Jr. , who played Sandy, just revealed that he was the producers' second choice to play the male nanny (or "manny" as he was oh-so-hilariously dubbed in the show). He only got offered the role after Tom Hanks , the nicest man in America , turned out to be unavailable.

"I wasnt even supposed to be [Sandy], that was originally offered to Tom Hanks but he wasnt gonna make it back from his film on time," Prinze told EW . "And so my agent called me and said, 'Do you want to be on Friends?' And I said, 'Yeah, Ill do an episode of Friends. Thatll be great.' He said, 'Yeah, it shoots tomorrow.' And I was like, 'What?' He said, 'Yes, tomorrow, so Ill send you the script.'"

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Of course, even without Hanks, the show wasn't without its share of super-famous guest stars. Bruce Willis had an arc as Rachel's new boyfriend, who also happened to be the father of Ross' student girlfriend Elizabeth. Brad Pitt appeared as a man who loathed Rachel, a joke which only worked because the entire world knew that he and Jennifer Aniston were married in real life, while Winona Ryder played an old college friend of Rachel's.

Denise Richards played Ross and Monica's cousin, and Elle McPherson had a multi-episode stint as Joey's new roommate who eventually became his girlfriend. Reese Witherspoon and Christina Applegate both had guest roles as Rachel's sisters Jill and Amy, and when the show flew across the pond to London for Ross and Emily's wedding, Emily's mother was played by none other than Jennifer Saunders.

As the series progressed, the stunt casting got more and more absurd, but perhaps nothing will top the moment from early on in the show's run where Billy Crystal and Robin Williams appeared in the cold open; a spur-of-the-moment creative decision made solely because the two actors happened to be in the building, and which remains one of the most surreal scenes in Friends history.