When Rivers Cuomo penned the opening lyrics to Weezer's "Buddy Holly," he probably never imagined he'd be making a fan out of R&B/hip-hop producer/songwriter Jermaine Dupri.

"When I heard Rivers saying, 'What's with the homies dissin' my girl/Why do they got to front,' I became a big fan," says the Atlanta-based music mogul, who has crafted tunes for major artists like Usher, Mariah Carey and Janet Jackson. "He was talking my type of language in a rock record and it always stayed with me. They talk like I do, but to a different crowd—we're basically speaking the same words."

The admiration has now turned into collaboration, with Dupri getting a songwriter's credit on Weezer's latest album, "Raditude," released Nov. 3 on Geffen Records. Dupri talked to Billboard about jumping genres in his songwriting—and how his label, So So Def, is expanding into branding.

This is the first time you ventured outside of hip-hop and R&B and wrote for a rock act. How did "I Can't Stop Partying" come about?

I was in the studio one night and I was on my wild shit, like, "I can't stop partying"—that's exactly how I felt that night. Like, "This is my life. This is what's going on." So, I recorded myself playing the drums and singing, freestyling, and then I had my engineer put some guitar licks on there. I immediately got into it and I asked someone to get it to Weezer.

Were you just trying your luck? Or did you really think Weezer would go for it?

I didn't think they'd do the song at all. This is the first time someone's taken a song I wrote from a different genre—it was a shot in the dark.

Plus, I'd done this a hundred times before—I go in the studio, I write what I'm feeling, and sometimes I just throw that stuff away. That's actually what happened with [Usher's] "Confessions"—that's what I was going through at the time: I had to confess to my girl I had a baby by someone else. I write songs all the time and don't give them to others, but this time I talked to [producer] Dallas Austin and I told him I had rock songs that I wanted to get placed.

Have you always been a rock fan?

Click here for the full Q&A which includes his upcoming projects, plans for his So So Def label, how his collaboration with Weezer evolved, and more.