Charlie Puth was pleasantly surprised to learn that teen heartthrob Shawn Mendes writes his own material.

The Marvin Gaye singer served as the support act for Mendes' Illuminate World Tour, during which he played to sold-out crowds across the country.

During their trek, the two pop stars spent some downtime together bonding over their mutual love of John Mayer and P Diddy, and even the odd jam session, which proved revelatory to the 26-year-old.

"We vibed out with John Mayer," Puth recalled in an interview with Billboard Magazine. "I was showing him Kirk Franklin, Gospel music, Baptist choirs, and he was showing me - he was like, 'Do you know this song, I'll Be Watching You by P Diddy?' I'm like, 'Yeah, I know that song, Shawn, who was born in 1998.' (Laughs.) But he was actually schooling me on stuff too. I hadn't heard some of these rock records. He has great taste in music."

Their bonding sessions ended up evolving into impromptu writing sessions and Puth shared that they "started something really cool" together, but fans of the pair may have to wait some time until it surfaces, as their hectic tour schedules got in the way.

But Puth didn't rule out the possibility of a collaboration with 19-year-old Mendes in the future and praised the star for his all-round musical ability, which he admits he was a little surprised by.

"He'll hate me for saying this, but I just assumed he had other people writing most of his material," Puth shared. "But when he sat down and just started singing melodies, kind of like I did, I was like, 'Wow! That's really impressive.' Don't judge a book by its cover."

The Attention singer is currently working on his sophomore album, Voicenotes, which is set to debut in 2018 and has just announced he'll be heading out on The Voicenotes Tour with Hailee Steinfeld in support of the album next year, with stops all over North America starting from July.