"I think I'm bigger and I weigh more," Mendes -- who released his new single "If I Can’t Have You" on Friday -- replied. "I think he has another, like, type of level that he can click into that I don't have. I don't possess the switch that I think he [has]."
"Hmm, Gonna have to break a few more records to dethrone my title there bud (Canadian voice)," Bieber wrote on Mendes' post. "But if you want we can play hockey for it but I heard your [sic] a real bender on the ice we could just drop the buckets and tilt for it."
Mendes replied to Bieber, writing, "LOL any time any day you just let me know!!!!!"
The cover was brought up during his interview with host Elvis Duran, where Mendes revealed that he questioned whether to share it or not, but found Bieber's comment hilarious.
"I'm not going to lie, when I got the photo from that paper I was like, 'Should I post this? I don't want people to think I'm saying I'm the prince of pop. It’s just what the headline said and the photo, and there's other princes of pop like Bieber,'" he explained. "I was like, 'No, I’m just going to do it. It's no big deal.' The second I posted it, I was like, 'Shouldn’t have done that!'"
The singer -- who attended last year's Met Gala with Bieber's now-wife, Hailey Baldwin, before claiming the two were "just friends" -- added, "[Bieber] is so funny…I honestly pretty much live to read the comments he posts."
Mendes, meanwhile, is promoting his new music and in another interview with Zane Lowe on Best of the Week on Beats 1 on Apple Music, revealed that he originally thought his single "I Can't Have You" would be perfect for fellow pop star Dua Lipa, before taking it on.
"I wrote this song, actually, a really long time ago in my condo with Scott Harris. We wrote a ton of songs. I was back in the studio with Teddy Geiger and Nate and I was playing it on piano and I was like, 'Oh my god, this would be really cool for Dua Lipa," he confessed. However, after changing the instruments and working more on the song he realized that he didn't know if he could give the song away.
"A couple weeks later, I’m in the studio with Scott playing it again and I go, 'Dude, this is really serious. I don’t know if I can ask Dua to sing it," he said. "Though that would’ve been incredible, I said, 'I think I gotta go all the way with this.'" The rest is history.