Two weeks ago, Skylar Grey got an email asking her to sign some paperwork. It was the first indication she had that she'd wind up on Eminem's new Marshall Mathers LP 2, one of hip-hop's most highly anticipated releases of the end of the year. The track, "Asshole," was originally created more than a year ago on a trip to Detroit with producer Alex Da Kid.

"I knew [Em] wrote verses to it a year ago or whatever, but as far as I knew, he wasn't going to use it," she said, laughing, in a phone called with XXL. "And then two weeks before the album came out, I got [that] email. I didn't even know until a couple weeks ago that he was even gonna use the song."

The the song's inclusion was a bit of a surprise, it could hardly be considered out of left field. Grey has been a frequent collaborator with Em over the past few years, co-writing the Rihanna-assisted "Love The Way You Lie" and co-writing and singing the hook on Dr. Dre's single "I Need A Doctor," which featured Em. She's also showed up on the first Slaughterhouse record, and called in Shady to executive produce her last album, Don't Look Down.

"He's got a really good ear and I really trust him on a creative level," she said about those Don't Look Down sessions. "I'm easily swayed by people's opinions, and to have a lot of people around you—label, producers, managers, and all that stuff—it can get a little confusing, 'cause everybody has their own idea of what it should sound like. I wanted Em to be the one person who I actually trusted."

So when in Detroit writing songs for her album, she stopped by the studio with Eminem, giving him song ideas and hooks. It was during that trip, while sitting in her hotel room, that she wrote the hook for "Asshole." "Usually what happens is, I write hooks to different beats and I'll give him a few, he'll like one of them, and he happened to like that one," she said about the story behind the track. "I hadn't really planned on, 'Oh, I need to write a song about an asshole.' That's just not the way it works. It's just the way the melody just came out of my mouth with those lyrics, it just kind of flowed. It's like freestyling almost. I didn't plan it, it just happened."

The song—like many on MMLP 2—contains an extended lyrical assault by Shady, who switches up flows effortlessly. "He doesn't follow typical formulas for songs, and I love that," Grey said. "That's the ultimate artistic freedom, I think."

Grey also accompanied Em on his recent Saturday Night Live performance, joining him on stage for "Survival," where Em's atypical song structure nearly tripped her up. "When I was learning the song I was like, 'Wait a second, the first verse is actually shorter than the second and third,'" she explained, laughing. "They're extended verses, and I had to figure out where the timing was of when the hook came back in, and it wasn't typical at all."

With a January tour on the horizon, Grey has been back in the studio working with other people, though she's reticent to say who: a collaboration with Moby from his recent album and a recent song with Kaskade saw her take the stage with both in recent months. But it's one of the bonus tracks on MMLP 2 that's got her really excited: "Wicked Ways" includes the line, "By the way thoughts are getting darker by the day / I'm a combination of Skylar Grey, Tyler the Creator, and Violent Jay / It's a fucking miracle to be this lyrical." "I've always wanted a shout out from Em," she explained, adding, "it was another little dream come true." —Dan Rys (@danrys)