It's a sad day in the rock world. Tenacious D, the "greatest band in the world," have officially given up their rock roots for Jazz. Yes, it's true. The duo exchanged their guitars for beret's and black turtlenecks. Witness the transformation below, where The D sat down for an interview with Craig Ferguson explaining the transformation along with the live debut of their upcoming Record Store Day Black Friday release, "Simply Jazz": (via The Audio Perv)

*Watch Tenacious D's Radio 104.5 Studio Session HERE.