These days, it's hard to surprise fans at a rap concert when the artist they've come to see brings another performer onstage because they come to the venue expecting it. However, A$AP Rocky surprised the crowd when he brought out Yasiin Bey, aka Mos Def, during a show at XOYO in London on Saturday (April 4).

A fan caught the moment in a video, which was uploaded to YouTube. The Black Star member appears onstage causing the crowd to go absolutely crazy. In fact, people react so passionately to his appearance that Yasiin had to tell folks to back up and calm down a bit before he began performing.

After a few long pauses, the instrumental to his hit song "Ms. Fat Booty" dropped, but the rapper chose not to spit any verses. He did kick a few lines of "Universal Magnetic," however, much to the crowd's delight.

From there, Rocky deemed the night historic since he and the Brooklyn MC stepped onstage together for what appeared to be the first time.

There's a good chance the hyped crowd thought Yasiin and A$AP were eventually going to perform together but that didn't happen. Instead, the Harlem spitter played a new track off his upcoming album, At.Long.Last.A$AP, which seemed to be well-received.

In a recent interview with Complex, Rocky said that he took his time making this sophomore album and he's in the most creative place he's ever been in his life.

"I needed time to master my craft," he stated. "You don't rush art, and I don't think you quickly produce fine art. You take your time. That's not an excuse, or me trying to justify [anything], that's truly what I believe."

Watch Yasiin Bey hit the stage with Rocky above.

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