The two country stars seemingly met up during one of Zach's recent tour-stops.
Also set to take the Bridgestone Arena stage on November 8 is Megan Moroney, Old Dominion, Luke Bryan, Carly Pearce, K. Michelle, Little Big Town and Tanya Tucker.
The ‘Heartache Medication’ hitmaker performed a number of songs as part of the special celebration.
They'll be joined by Shovels & Rope, Fleet Foxes, Grace Potter, The Flaming Lips and more.
They'll be joined on the impressive line-up by the likes of Midland, 49 Winchester, Morgan Wade and more.
The duo released the fan-favourite song at the start of the year.
