This is a hip-hop heads' dream come true. Yasiin Bey aka Mos Def surprised fans in Montreal when he joined headliner Kendrick Lamar onstage at the 2015 Osheaga Festival on Saturday (Aug. 1).

Kendrick spit the first few verses from his To Pimp a Butterfly heater "Alright," which was accompanied by fireworks and a dancing Yasiin Bey rocking out.

But, halfway through his performance, K. Dot asked the Brooklynite to join in on the lyrical fun.

"Bey. Bey. Can you talk to 'em for a second? Just speak some words for them," the Compton rapper said.

In a rare treat, he played on Kendrick's lyrics by rapping, "We don' been alright" and "We already alright" in place of the original lines "We gon' be alright."

The To Pimp a Butterfly creator was smiling from ear to ear as the former Black Star member flipped the chorus.

The artist formerly known as Mos Def bounced around the stage, feeling the drums and soaking in the energy from the crowd.

He continued to play around with the lyrics for the second half of the song's performance. "Brooklyn, Compton we already alright," he rapped.  "Kendrick in the house tonight. Yasiin in the house tonight."

Before his set was over, Kendrick revealed to the Montreal audience that Yasiin Bey inspired him to begin rapping.

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