Chavela Vargas is a household name in Mexico but many Americans aren't privy to one of the most passionate performers of the last century. The queer masculine-presenting singer was prized for her tragic, tearful emoting—her songs appear in Pedro Almodovar films like Flower of My Secret.

But she's also infamous for one of her paramours: Artist Frida Kahlo.

Vargas, who died in in 2012 at age 93, is the subject of Chavela, a fascinating new documentary opening in select theaters on Friday. Out filmmaker Catherine Gund (Born to Fly, What's On Your Plate?) says Mexican audiences laughed, cried, and sang along when Chavela was on-screen in the doc, which played to huge theaters.

But in the States, Gun often has to mention Kahlo to elicit a response. "For Frida Kahlo to have chosen this person, she must have been magical," Gund tells NewNowNext. "And that's the truth–she was."

Gund first met Chavela Vargas, born Isabel Vargas Lizano, in Mexico in 1991. She spent two days with the singer, going backstage at a concert and visiting her home, where Vargas spoke candidly about her life and career with a group of young lesbian feminists. (Vargas officially came out at age 81 in her 2000 memoir If You Want to Know About My Past.)

This previously unseen footage is the heart of Chavela, along with interviews with those who knew her, including Almodóvar, fashion designer Elena Benarroch, pop singer Miguel Bosé, and women's rights activist Alicia Elena Pérez Duarte y Noroña, who was one of Vargas' former lovers.

"I thought, 'We're kind of doing this interview because people don't want to lose your story,'" Gund says. "We didn't know–maybe she did–that she was going to go on to continued greatness—a bigger and better third chapter."

The interview is incredibly candid: The singer is relaxed and open, touching on her love of women (Kahlo included) and how her early attempts at making her stage persona more "femme' failed miserably. Vargas always preferred pants and ponchos to typical women's ranchera wear, and she sang in a booming, raspy alto (often explicitly about heartbreak and ache caused by other women).

"I didn't know at time how special that interview really was," says Gund. "She was at such a striking moment where she'd just gotten sober, the love of her life had just broken up with her, and she was surrounded by young lesbian feminists who knew her and loved her."

Alcoholism derailed Vargas' career for nearly 15 years—she only returned to the stage the same year as Gund's interview, performing at a bohemian nightclub in Coyoacán. As the cameras roll, she isn't yet enveloped in that protective aura that keeps many stars from revealing too much.

"When I interviewed her, she'd never been to Spain yet; she hadn't played on a big stage; she hadn't met Pedro Almodovar," Gund says. "Even though she was 71, she was only halfway through."

It wasn't until Almodovar brought her to Spain some years later that Vargas became internationally recognized for her music. A Carnegie Hall performance followed in 2003. And by then, she felt, it was safe to come out publicly.

"I think she was always out," Gund says. "But when she got the surge of the tidal wave of international queer community movement behind her at 81... suddenly it was sort of a tipping point and she was able to use the terminology. To me, she was never hiding."

Vargas actually refused the label of lesbian when speaking with Gund in 1991.

"She couldn't embrace that word—[to her] that was used to make her feel less than and to put her down," says Gund. "But she was totally open about her lovers and she never got married or had a beard or children just to make it seem like she was heterosexual. While she wasn't using the most contemporary terminology to self-identify, she never said that wasn't who she was. That's not just a semantic difference."

Vargas's authenticity and her struggles are felt through her music—She's often referred to as "The Rough Voice of Tenderness." She'd had a difficult childhood and a distant mother, and years of drinking took a toll on her relationships (namely with Duarte y Noroña, as she laments in the film).

"[she] said, 'It was pain and suffering but I took it and put it on the stage and you all find it beautiful,'" says Gund. "And, somehow, that's how she survived. That's why she kept singing... it was her way to survive."

But unlike others, Vargas never seemed to struggle with her sexual identity–she just couldn't be as open about it in Catholic Mexico.

Gund was conscious of how important Vargas's legacy is to her adopted homeland, and says she tried to strike a balance with how much Chavela put her queerness front and center. Yet, she adds, Vargas enjoyed being an icon to young Mexican lesbians who had no other idols to look up to.

"That's why we interviewed her in the very first place. We don't have anyone else."

Chavela opens October 4.