Jimmy Fallon's campaign to sing with nearly every living rock legend just struck gold. On his show last night (Sept. 26), he performed with Robert Plant, who stopped by to promote his newest effort, 'lullaby...And the Ceaseless Roar.'

During the interview segment, Plant acceeed to Fallon's request to perform a duet, as you can see in the video -- which also features Plant making a lewd joke about the shape of the microphones -- above. With the help of an iPad and an app that allows for sounds to be looped, they created a three-part harmony bed of Gene Chandler's 1962 doo-wop No. 1 smash, 'Duke of Earl.' Plant and Fallon then took turns singing lead.

Six months ago, Fallon and Billy Joel sang the Tokens' 'The Lion Sleeps Tonight,' also with the help of the looping app. Coincidentally, 'Duke of Earl' was referenced by Joel in his 1983 hit, 'Keeping the Faith.'

In addition to singing 'Rainbow,' Plant and the Sensational Space Shifters also did a web-only performance of 'Turn It Up.' The video can be found below.

Watch Robert Plant Sing 'Rainbow'

Watch Robert Plant Sing 'Turn It Up'