It's been an awfully long time coming, but when Neil Young guested on 'The Tonight Show Starring Jimmy Fallon' on Feb. 3, he finally had a chance to sing a duet with ... Neil Young.

As fans are no doubt already aware, Fallon has made something of a habit out of impersonating Young over the years, using his wardrobe department and his knack for vocal mimicry to apply Young's trademark yowl to all kinds of odd-seeming songs -- and often with the assistance of Young's peers and friends, as he did when he brought "Neil" out to sing alongside Bruce Springsteen, David Crosby and Graham Nash (watch that one here), and Crosby, Stills and Nash (video here).

After Young and Fallon's joint rendition of the 'Harvest' track 'Old Man,' which you can watch via the video embed above, Young offered his public blessing for Fallon's bit, joking, "I saw you doing me before and I always thought it was unbelievable. This is the most I've been on TV, ever."

Young also sat in with Fallon's house band, the Roots -- who were joined by former 'Tonight Show' bandleader Doc Severinsen for the evening -- to run through 'Who's Gonna Stand Up?,' the single from Young's recent orchestral 'Storytone' project. Check out that performance below.

Watch Neil Young Perform 'Who's Gonna Stand Up?' with the Roots

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