Taylor Swift 'Became This Girl' In 'I Knew You Were Trouble' Video

She was '100 percent in,' director Anthony Mandler says of Swift's role in her dark new clip.

Working with artists who want to push the envelope is nothing new for Anthony Mandler: just this year alone he's directed videos like Lana Del Rey's "National Anthem" (in which she and A$AP Rocky portray Jackie O and JFK), Fun.'s "Some Nights" (where Nate Reuss's internal struggles are fought on a Civil War battlefield) and Rihanna's "Diamonds" (which deconstructed her life into a series of dreamlike vignettes).

But when he heard Taylor Swift wanted to get dark on her new "I Knew You Were Trouble" video, well, even he was a bit surprised.

"To be frank, she came to me with the intention of doing something completely different, and that was the mantra from the beginning: 'I want to do something that is radically different, I want to play a character, I want to be somebody else, and I want to tell a really intense story that people can relate to,'" Mandler told MTV News. "So, that's how we started, and then the process was 'Okay, what's the story and how far can we actually go? What was she actually comfortable with? And what was maybe pushing too far?'"

And while "Trouble" is definitely a departure for Swift, Mandler says that his star never wavered from her original idea: she wanted to go as far as possible, and tell a story of a doomed love and a good girl pushed to the brink.

"She really stepped into this character, she became this girl," he said. "She was able to embrace this journey and let go of Taylor Swift for a couple days and be somebody else. She was one-hundred-percent in. She and [co-star] Reeve [Carney] just went for it."

Mandler drew inspiration from his previous work — like the Killers' "When You Were Young," Lana Del Rey's "Ride" and Muse's "Madness" — to create something that was "cinematic to a different level," though when it came time to write the narration that bookends "Trouble," well, he relied solely on Swift ... and once again, he was blown away by the results.

"At the end of the shoot, we sat in the car and kind of riffed lines back and forth," he explained. "I wanted to do it right after the shoot was over so she was in that headspace, and just let her talk free-form, and then I organized it later on and cut it together. And I was amazed by just how well she understood this character."

And at this point in his career, after working with the biggest names in the business, Mandlers said it's projects like "Trouble" that keep him coming back to music videos. He realized Swift was willing to take risks, and, in the process, perhaps take a massive step as an artist. And that goes beyond merely making another video.

"I think that the Rihanna's, the Beyonce's, the Jay-Z's, they're always willing to tear things down and re-create themselves," he said. "[And] I'm hoping is that this is the first moment in a new chapter for Taylor, that this is a left turn on her path that will lead to new and different things ... it will give her the confidence and power to to do different things, to be able to broaden and take her fanbase on a journey that's unexpected. And that is, to me, what prolongs people's careers."

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