"The Best Was Caligula," says the actress. "Everyone Was Naked"
Credit: Penthouse Films International/Everett Collection

She may have one of Hollywood’s most enviable bodies but Helen Mirren, 70, says baring skin for a film was something she always feared.

“I was always afraid. Always,” the Trumbo actress tells PEOPLE. “It’s not fun to be on a film set and be one of the only ones naked.”

Mirren says the only time she didn’t mind doing a nude scene was in the graphic 1979 film Caligula.

“Everyone was naked in that. It was like showing up for a nudist camp every day. You felt embarrassed if you had your clothes on in that movie.”

For more on Helen Mirren’s revealing interview, pick up the latest issue of PEOPLE on stands Friday.

But Mirren says her past nude scenes are nothing compared to what is seen in films today.

“It has become so commonplace now,” says Mirren.