There are plenty of rap duos who have an indelible natural chemistry: OutKast and Mobb Deep come to mind, pairs that broke onto the national scene together. Then there are those that worked beautifully despite being label-arranged marriages, like when Mos Def and Talib Kweli teamed up as Black Star. But few rappers have what Eminem and 50 Cent found, a special synergy despite meeting one another at different points in their respective careers. And according to a radio appearance the latter made back in September 2015, they almost got to display that relationship on a huge national platform last year.

As per 50's interview with former NFL quarterback Boomer Esiason and Craig Carton on sports radio in New York, he and Eminem were offered "See You Again," the song for the film Furious 7 that served as a de facto tribute to the actor Paul Walker, who passed away in a car accident before the last franchise installment was completed.

“At the time we had to make a decision between doing [the soundtrack for the boxing movie Southpaw] and the song for Fast & Furious," 50 said. "And ["See You Again"] was a huge success for Wiz Khalifa and them. [Eminem] decided to do Southpaw because he was invested in the project."

50's right about "See You Again" being "a huge success": Last fall, it became the first American rap song to reach 1 billion views on YouTube. It also spent 12 weeks atop the Billboard singles charts, which ties it with the biggest hit of Eminem's career, "Lose Yourself." That song was also included on a soundtrack to a movie--8 Mile, in which he played a fictionalized version of himself.

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