Neil Young couldn't make it for an appearance by Crosby Stills and Nash on the 'Tonight Show' to promote the new 'CSNY 1974' box set. But that doesn't mean he wasn't there in spirit: Host Jimmy Fallon once again assumed the role, joining CSN for an utterly hilarious cover of 'Fancy,' the pop hit by Iggy Azalea and Charli XCX.

The TV host, doing a dead-on Young, takes the initial verse and chorus before David Crosby, Stephen Stills and Graham Nash join him on stage -- just in time to harmonize on a line about getting trashed from a minibar. (A smiling Crosby can hardly contain himself.) The group then ends with a flourish, tacking on an ending straight out of 'Suite: Judy Blue Eyes.'

Later, the trio returned -- sans "Young" -- for more straight-forward readings of a pair of classics, 'Teach Your Children' and 'So Begins the Task.' 'CSNY 1974,' featuring a series of long-sought-after concert recordings, is out now.

Fallon memorably appeared as "Young" with Crosby and Nash for a similarly oddball cover of 'Party in the U.S.A.' by Miley Cyrus on an earlier Tonight Show episode.

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