See Bob Weir and John Mayer's 'Long, Strange' 'Truckin'' Jam

Mayer, who guest-hosted the 'Late Late Show,' also sat in on "Althea" with the guitarist

With a Grateful Dead reunion on the horizon, guitarist Bob Weir appeared as the musical guest Thursday night on The Late Late Show to jam on "Truckin'" with guest-host John Mayer. The latter introduced Weir while standing just to his right, and they quickly settled into a groove with the rest of the band, trading bluesy guitar licks. Later in the broadcast, they returned for a run-through of the Dead's "Althea" (streaming below) which also featured Mayer's fluid guitar soloing throughout.

This summer, the Dead will play three 50th anniversary reunion shows in Chicago. The band has said the gigs, which will take place from July 3rd to the 5th, will be its last-ever performances. Phish's Trey Anastasio will be on hand to help out, as will Bruce Hornsby, who will play piano.

Mayer served as Late Late Show host earlier in the week as well, as the program readies itself for James Corden to step in as host on March 23rd. Earlier in the week, Mediaite reported the singer and guitarist brought out some interesting guests for their first-ever TV interview: Katy Perry's Super Bowl sharks.

"We're lucky to have them here tonight," in his intro. The pair walked out – with some guidance from a "marine biologist" – and eventually settled onto the Late Late Show couch. Mayer asked the sharks about becoming a viral phenomenon, after which they just looked at each other, and the biologist explained, "They can't talk, John. They're sharks, they're not dolphins." They joked about the agility of the sharks, and John attempted to cajole them into dancing, though the results were not quite what he expected.