Yesterday Chance The Rapper hosted TIP Fest, a free festival for high schoolers and college students (ages 13–24, because that's not a recipe for madness), at Chicago's Northerly Island.

Besides a headline slot from Chance-affiliates Donnie Trumpet and The Social Experiment there was a surprise guest appearance from none other than Kendrick Lamar. He stepped in with Chance to perform two tracks, 'm.A.A.d city' and 'i'.

Here's a video of that as tweeted from hip hop blog, Lyrical Lemonade: