There were plenty of surprises at the BET Music Matters Showcase at SXSW in Austin, TX on Thursday (March 14). During T.I.'s headlining set, Kendrick Lamar jumped onstage for a memorable performance of their collaborative tune, 'Memories Back Then,' from Tip's 'Trouble Man: Heavy Is the Head' album.

As witnessed by BET, T.I. was performing the song and wondered aloud of how cool it would be if K.Dot could joined him to perform his verse on the song. And instantly, Lamar appears onstage and wows the crowd with his lines from the track. Tip then allowed the Compton rapper to perform 'Swimming Pools' and 'Backseat Freestyle' from his celebrated album, 'good kid, m.A.A.d city.'

Also joining T.I. onstage that night was Pharrell Williams, who assisted the Atlanta rapper on their rendition of 'What You Know.'

The BET Music Matters Showcase also featured stellar performances from Bridget Kelly, Joey Bada$$, Chrisette Michele, BJ the Chicago Kid, LeCrae and Schoolboy Q.