Eminem at Lollapalooza

Eminem at Lollapalooza 2014

Theo Wargo, Getty Images

Six days before Eminem and Rihanna are set to combine for the first date on their co-headlining Monster duo, the superstar pair gave music fans a quick preview of the upcoming stadium shows when Em brought out Rihanna as a surprise guest during his Lollapalooza headlining set on Friday night (Aug. 7).

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The rapper and singer linked up for both of their smash collaborations, serenading Chicago's Grant Park with "Love The Way You Lie" and "The Monster." Both songs enjoyed multi-week runs atop Billboard's Hot 100 chart. Rihanna also joined Em to handle Dido's memorable hook on his 1999 hit, "Stan."

The guest appearance highlighted Eminem's first headlining set at Lollapalooza since 2011. But Rihanna wasn't Eminem's only surprise. He also brought out frequent collaborator Royce da 5'9".

At the beginning of the night, before Eminem made his big entrance, a video played, explaining that Matthew Mitchell -- Stan's brother -- had kidnapped Em, with interviews from the detectives on the case, as well as Stan and Matthew's "mother."

Along with early favorites like "Bizness" and "Kill You," Slim Shady dove into cuts from last year's "The Marshall Mathers LP II," which topped the Billboard 200 chart upon its release. "The Monster," his second Rihanna collaboration, is "MMLP2's" biggest hit to date. "My Name Is," and "The Real Slim Shady" also made the bill -- to the delight of the large crowd. 

Eminem closed his Lolla performance with "Not Afraid," from Recovery, dedicating it to "anyone who's ever lost someone." He then broke out into "Lose Yourself," while a screen showed a burning Detroit in the background.

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The Monster tour kicks off this Thursday, Aug. 7 at the Rose Bowl in Pasadena, Calif.

Live at Lollapalooza 2014