The Doobie Brothers aren't finished working with big-name guest artists. On the heels of 'Southbound,' a double album of songs recorded with many of today's country stars, the Doobies have announced a joint appearance with the jam band String Cheese Incident.

Creatively renamed the Doobie Incident, this pairing is among the first confirmed performers at the 2015 Lockn' Music Festival, to be held Sept. 17-20 in Arrington, Va. The always-game String Cheese Incident have previously worked with the Doobies' 'Southbound' collaborator Zac Brown in 2013 and JT Taylor of Kool and the Gang in 2014.

Also already confirmed for Lockn' in 2015 are the Tedeschi Trucks Band, featuring former Allman Brothers Band member Derek Trucks, Widespread Panic and Keller Williams' Grateful Gospel, a Grateful Dead-themed group.

On 'Southbound," Tom Johnston, Michael McDonald and Patrick Simmons perform on a Doobie Brothers album for the first time since 1978's 'Minute by Minute.' In addition to Brown (who sits in on a new take on 'Black Water'), the Doobies are joined by Blake Shelton ('Listen to the Music'), Toby Keith ("Long Train Runnin''), Sara Evans ('What a Fool Believes') and others.

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