Robert Plant joins singing -- but definitely, definitely not married -- partner Patty Griffin for three songs on her forthcoming solo album 'American Kid,' continuing a collaboration that began with 2010's well-received 'Band of Joy.'

The duo gave a preview of their new work last December, performing "Ohio" and "Gonna Miss You When You're Gone" -- a pair of tracks now scheduled for inclusion on 'American Kid' -- during a joint appearance at a benefit show in Austin.

Griffin's newest album, her seventh, was produced by Craig Ross -- perhaps best known for his guitar work with Lisa Germano, 1980s-era violinist with John Mellencamp. Ross also helmed Griffin's 2004 album 'Impossible Dream.' Recorded in Memphis, 'American Kid' is due on May 7 via New West.

Plant said in published reports last year that he had eloped to Texas with Griffin, but that quote was later denied by his representatives. Whatever their living arrangements, they remain one busy couple: Plant and Griffin toured in the summer of 2012 with a group called the Sensational Shape Shifters, and have already announced a new Band of Joy album for later in 2013, as well.

Robert Plant and Patty Griffin Sing 'Houses of the Holy' With Band of Joy