Rosie O'Donnell says Whoopi Goldberg is 'meaner than anyone' she's ever encountered on television

An "angry letter" allegedly written by Whoopi Goldberg to Rosie O'Donnell appears to confirm the long-rumoured feud between the two comedians.

The letter, written back in 2009, was recently brought to light by O'Donnell, who was interviewed by author Ramin Setoodeh for his new book Ladies Who Punch: The Explosive Inside Story of The View.

The stars were co-hosts on US talk show The View in 2009 and again in 2014, when O'Donnell was brought back to replace outgoing host Barbara Walters. But tensions had been brewing in the seven years since Goldberg and O'Donnell were on the show together.

According to O'Donnell, she and Goldberg clashed in 2009 over the rape allegations against Hollywood director Roman Polanski. It didn't sit well with O'Donnell after Goldberg implied that Polanski hadn't committed "rape rape" on a minor -- despite pleading guilty to statutory rape -- and the pair clashed on camera. That's when O'Donnell said that she received the "angry letter" from the Oscar winner.

"I'm sorry if that hurt your feelings," O'Donnell wrote back to Goldberg, as revealed in Ladies Who Punch. "I have different feelings about it than you. And I stand up for what I believe, but I'll never bet against you, Whoopi Goldberg."

However, when O'Donnell returned to The View in 2009, their relationship was all but over.

"Some people would say, 'What's going on with you and Whoopi?'" O'Donnell recalled in Setoodeh's tell-all book. "I was like, 'Are you watching the show? It's pretty much right there.' I have no desire for a public feud."

The pair weren't only frosty towards each other on camera -- it was the same story behind the scenes. O'Donnell claimed in the book that all her suggestions were shut down. Her idea to start morning meetings 30 minutes earlier was not welcomed, and likewise her pleas to cover the Bill Cosby rape case were not well received.

"Whoopi Goldberg was as mean as anyone has ever been on television to me, personally -- while I was sitting there," O'Donnell told Setoodeh. "Worse than Fox News. The worst experience I've ever had on live television was interacting with her.

"She's a minority, feminist, smart, funny, groundbreaking legend who is black in America," O'Donnell added. "I'm never going to not have respect for Whoopi Goldberg. But that was a painful experience, personally and professionally."