You can imagine how the conversation went, and we're pretty sure both parties were thrilled with the proposition of trying out each other's machines. Rossi famously tested Michael Schumacher's Ferrari all the way back in 2007. He did very well, just 0.7 seconds off the pace of the front runners.
Hamilton has also ridden Yamaha superbikes in the past, and was even told to slow down a bit by his mentor Alex Lowes!
You can see the video here on the MotoGP website