This is dark — even for The Dark Knight.

A woman who worked for legendary comic-book writer Frank Miller says she was put through hell by the “Batman” scribe’s gal pal.

In a Manhattan Supreme Court lawsuit, Joanna Gallardo-Mills, 41, says Miller’s the “Sin City” creator’s girlfriend, Kimberly Cox, smeared her work area with feces, destroyed her printer with a hammer, threw phones at her, and even left a used feminine hygiene pad by her desk.

“Nobody should have to work under those conditions,” said her lawyer, high-powered employment attorney Matthew Blit.

Gallardo-Mills claims she was canned for complaining about how Cox was treating her.

The suit says Gallardo-Mills went to work for Miller — whose 1986 Batman comic series “The Dark Knight Returns” is considered revolutionary — as an executive coordinator in November 2008.

The Philippines native said it wasn’t long before there were problems with Cox, Miller’s much-younger actress girlfriend.

Cox soon made it clear she had issues with Gallardo-Mills, yelling things like, “I can’t understand your funky accent. Speak f–king English,” the suit says.

The suit notes Gallardo-Mills “has lived in the United States for over 20 years, is fully fluent in English, and only spoke English in her professional capacity” with Miller.

Cox yesterday said she was “shocked” by the suit.

“We didn’t know this was going forward because she was offered a very heavy settlement and declined,” she said.

Gallardo-Mills’ work situation went in the toilet In July 2010, when Cox allegedly threw a phone and chair at Gallardo-Mills — and “smeared human feces” on a countertop in her work area in the Hell’s Kitchen living/work space that Miller and Cox shared, the suit says.

A year later, Cox went on another rampage, the suit says, scattering all of Gallardo-Mills’ files across the floor and destroying her printer “with a hammer,” the suit says.

Then, Cox left her filthy underwear and “used menstrual pad” in her work space, the suit says.

After Gallardo-Mills complained, Miller eventually agreed to let her work out of her home to keep her away from Cox.

She’s seeking unspecified money damages from Miller and Cox for discrimination and “mental anguish.”

A rep for Miller did not return a call for comment.

Additional reporting by Liz Sadler and Dareh Gregorian