Yasiin Bey (Mos Def) Joined Kendrick Lamar for 'Alright' Performance at Osheaga

Josh Brasted/FilmMagic
Kendrick Lamar performs on stage at the 2015 Essence Music Festival on July 5, 2015 in New Orleans, Louisiana.

Kendrick Lamar has been full of surprises this year. He was at it again during his headlining set at the Osheaga fest over the weekend, where the rapper introduced Yasiin Bey, aka Mos Def, on stage for an impromptu collab on his single "Alright," lifted from the album To Pimp a Butterfly.

Yasiin Bey, who Lamar cites as a key influence in his career, contributed a fresh set of lyrics to the song's chorus during the set in Montreal. 

Kendrick Lamar Goes 'Looney' Living the American Dream in 'For Free?' Video: Watch

Of course, Lamar dropped one of the biggest surprises in music this year when Butterfly, his second major-label album release, dropped unexpectedly on March 16 -- a week ahead of schedule. The album was a huge hit, landing at No. 1 on the Billboard 200 and peaking high on sales charts around the globe. The album also established Spotify's global first-day streaming record (9.6 million).

The official video for "Alright," in which Lamar catches more airtime than Michael Jordan did at the peak of his powers, arrived June 30. Watch the Osheaga performance below.