Chance The Rapper is full of surprises. Just a couple weeks ago, he shared the exciting news that he would be curating the first Teens in the Park festival in Chicago. Since he’s been hosting the successful on-going “Open Mike” sessions for teens in Chicago, there was no doubt that he would be up for this task too. However, the kids in attendance received a major surprise yesterday.

The free festival promised performances from local acts chosen by Chance himself, as well as Donnie Trumpet. But no one in the crowd could have expected to be surprised by Kendrick Lamar. Kendrick came out and performed “i” and “m.A.A.d. City” for an ecstatic crowd. We can only assume that the two planned this special surprise after their spontaneous joint performance with Earth, Wind and Fire and Bonnaroo.

View some more fan-shot footage below.