Alexander 23 Duets with John Mayer as Tour Wraps: 'An Honor to Share the Road with You'

Early arrivals to Monday's penultimate show of the Sob Rock Tour enjoyed an unexpected surprise.

"We actually have one more member tonight playing guitar with us," opener Alexander 23 told the crowd at Boston's TD Garden. "A warm welcome to my friend, John Mayer."

The musician, 44, then stepped onstage, joining the "Hate Me If It Helps" singer-songwriter, 27, for a performance of "Everybody Wants to Rule the World." The two traded guitar licks while Alexander 23 handled vocals on the Tears for Fears classic, impressing even the band themselves.

"Yes!! Honoured to have you both perform this. Incredible job," the English rockers commented on a YouTube video of the cover song.

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Thomas Falcone Alexander 23 and John Mayer

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After kicking off the beginning of the tour, Alexander 23's run was cut short after a COVID cluster broke out within Mayer's band. As soon as the postponed dates were rescheduled, however, Alexander 23 was back on the lineup, opening for the final four shows. He shared his gratitude for the opportunity on social media Thursday.

"If you know me at all, you know how much this means to me. thank you @johnmayer for being so gracious on and off the stage. it was an honor to share the road with you and your all star band," he wrote. "Many moments in my life (music related and otherwise) i have thought to myself 'i wonder what john would say about this?' i'm grateful to now have that answer just a text away."

He added, "Tears for fears on the sob rock tour. a fitting end to something i never wanted to end."

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Thomas Falcone John Mayer and Alexander 23

Alexander 23 recently told Billboard the two are now developing a friendship.

"He's inspired me in so many ways and continues to do so and it's cool to kind of pick his brain a bit. .... There's a huge attention to musicality at these shows that is really cool to see. We started a friendship there [that] I'm certainly grateful for. He's made it incredibly clear to say that he's here for me both professionally and emotionally, which is really, really cool."

The musician next heads to the UK and Ireland for a round of shows with Tate McRae before playing Lollapalooza, while Mayer links up with Dead & Company for their summer run kicking off next month.