Lisa Kudrow says life behind the cameras of the “Friends” set wasn’t always as warm and fuzzy as it looked onscreen … claiming the show’s writers’ room could be downright toxic — and even included alleged sexual talk about her costars.

The actress — who played Phoebe Buffay for all 10 seasons of the hit sitcom — opened up in a new interview with The Times of London … revealing the off-camera environment could get “mean” and “brutal.”

“There was definitely mean stuff going on behind the scenes,” Kudrow said.

And that wasn’t the most jaw-dropping part of her interview.

Kudrow claimed the writers’ room — which she said was made up of roughly 12 to 15 staffers, mostly men — would allegedly stay up late discussing sexual fantasies involving her costars Jennifer Aniston and Courteney Cox.

“We know that back in the room the guys would be up late discussing their sexual fantasies about Jennifer and Courteney,” she said. “It was intense.”

The accusations mirror a real-life legal fight tied to “Friends” back in 2004 … when former writers’ assistant Amaani Lyle sued Warner Bros. Television over alleged sexual and racial harassment after claiming she witnessed inappropriate conduct in the writers’ room. The case eventually reached the California Supreme Court, which ruled against her.

Even with the ugly memories, Kudrow made it clear she still loves the show — and especially cherished her time working with late costar Matthew Perry.

“Whatever any of us do in the future, we will never experience something like that again,” she said.