Noah Kahan fans were in for a huge surprise when Shawn Mendes joined the folk singer on stage for a duet.

Saturday, April 6 marked the first of three sold-out concerts in the city for Vermont-born singer songwirter Noah Kahan, with the latter two scheduled for April 14 and 15.

@jaclynforbes iconic duo #noahkahan #noahkahantoronto #toronto #shawnmendes ♬ original sound - jaclynforbes

What the 19,000-plus audience goers didn't know when they attended the concert Saturday, though, is that they were in for an extra special surprise: a guest appearance from Shawn Mendes.

The Pickering-born singer-songwriter joined Kahan on stage to sing his hit song Stick Season after Kahan introduced Mendes as a "north star," to him, and someone he's "looked up to a lot."

@jaclynforbes when @Noah Kahan is feeling sick so he brings out shawn mendes to help him sing stick season >>> #shawnmendes #stickseason #noahkahan #noahkahantoronto #torontotiktok ♬ original sound - jaclynforbes

Shawn Mendes is something of a fixture in Toronto, being a longtime resident of the city and making frequent appearances at locations and events, like in and around his King and Bathurst apartment or at the Beaches Jazz Festival.

Noah Kahan is currently on a Canadian tour, with stops in Ottawa, Montreal, Quebec City and London still to come.