Joan Rivers has called Lena Dunham "fat".

Speaking on shock jock Howard Stern's Sirius XM radio show, Joan ranted: "Lena Dunham, who I think is again terrific, how can she wear dresses above the knee?"

Howard replied: "Well, I think the thing we love about her is that she doesn't give a s**t ... She did a whole [Girls] episode in a bikini. It was the funniest f**king thing I ever saw."

His co-anchor added: "And it think that's what she's going for: Just because I don't look like a bikini girl, I want a bikini."

However, Joan bit back, saying: "But that's wrong. You're sending a message out to people saying, 'It's OK! Stay fat! Get diabetes. Everybody die. Lose your fingers.' "

Realising that the radio presenters weren't going to agree with her controversial opinions, the 80-year-old legend insisted that Lena could at least make more of an effort.

She scathingly said: "If you look the way you look, Lena, and that's fine and you're funny, don't say it's OK that other girls can look like this ... Try to look better."

Joan also couldn't resist taking one last dig about the 27-year-old comedienne's recent VOGUE cover, which has been accused of being excessively Photoshopped.

She quipped: "She was on VOGUE's cover looking gorgeous. You didn't know it was her."

Nevertheless, the E! News presenter insisted she was a fan of the talented and "funny" star.

Lena's constant nudity on the HBO show has been in the headlines over the course of its third series, with some questioning the point of her near-naked scenes.