WATCH: Shawn Mendes Joins John Mayer On Stage In Toronto

One night after performing at the JUNO Awards in Ottawa -- where he also picked up the Fan Choice Award -- Shawn Mendes was on stage in Toronto with John Mayer.

The 18-year-old singer was a surprise guest during Mayer's concert at the Air Canada Centre. The pair, on acoustic guitars, performed a mash-up of Mendes' hit "Mercy" and Mayer's 2008 track "In Your Atmosphere."

Mendes, who has long cited Mayer, 39, as a major influence, shared his excitement on Twitter.

"Damn. John Mayer is the best," he tweeted. "My job is the best. U guys are the best. What an insane night."

Last October, Mendes told Toronto Star writer Ryan Porter that he dreams of performing on stage with Mayer.

“I think I would be OK quitting the next day,” he said. “He’s the epitome of a musician that I would want to be.”

Fans shared video of the unexpected duet – which ended with a warm embrace – on social media.

Mayer's tour stops in Edmonton on April 17 and Vancouver on April 19. Mendes kicks off his Illuminate World Tour on April 27 in Glasgow and will be back home in Canada for a July 8 show in Vancouver. The tour also stops in Toronto and Montreal in August.

Watch fan-shot video of the pairing below: