Green Day just played a surprise show with Prima Donna in Milan, Italy

Moments ago, Green Day took the stage in Milan, Italy at a Prima Donna show to play a surprise set of songs. Prima Donna updated their Instagram with the picture to the right and the following caption.
Apparently, Mike tipped us off earlier today in this post on his Instagram.

We'll update this post as we learn more about the show...

Update 1: We've added the show into our tour section. As we get the setlist and photos, they will be posted there.