Steven Tyler Jams with Keith Urban

Keith Urban had definitely planned to play a bunch of Nashville honky-tonks Friday night (Sept. 6) to help promote the release of his new album, Fuse, coming out Tuesday (Sept. 10). But even Keith was surprised to see rocker Steven Tyler of Aerosmith in one of those honky-tonks, Tootsies.

Keith eventually called Steven up to the stage, introducing him as a "bad-a**ed blues legend singer" and the rocker called Keith "my favorite Idol." The two tore through ZZ Top's "LaGrange" and Aerosmith's hit "Walk This Way." And Steven even planted a kiss on Keith's cheek, meant for Keith to pass along to Jennifer Lopez, one of Keith's fellow judges for the next season of American Idol -- and one of Steven's fellow judges on a past season of Idol.

Steven said, "Give J-Lo this for me."