The pair collaborated together for a new comedic song entitled "Two Neil Youngs on a Tree Stump" about nature, time travel and why there were two Neil Young's present.
"We're two Neil Youngs sitting on a tree stump/ Used to be a tree trunk/ but look what we've done/ Said the father to the son," the duo sang with guitars in hand as they sat atop a revolving tree stump back-to-back inside a makeshift forest.
"Where did the other Neil come from? / Came from the future back to the past, to warn your [expletive]," they continued.
Fallon has continually impersonated the musician on The Tonight Show having previously performed as the 70-year-old in a number of skits including a performance alongside Crosby, Stills & Nash for a cover of Iggy Azalea's "Fancy."
Young is currently on a world tour in support of his new album Earth which features a mix of his previous work and nature sounds he recorded in his backyard.