The singer also confessed that he was friend-zoned several times by his now-girlfriend Camila Cabello, revealed if he ever spoke to Justin Bieber about attending the 2018 Met Gala with Hailey Baldwin and more.
Shawn Mendes is the latest celebrity to take part in Vanity Fair's popular Lie Detector Test video series -- and the singer's confessions did not disappoint.
As shown in a video posted to the magazine's YouTube channel on Monday, Shawn was hooked up to a lie detector and asked a wide variety of questions, with several focusing on his friendships with his celebrity pals -- including Taylor Swift, Justin Bieber and John Mayer -- as well as his relationship with Camila Cabello.
While the "Summer of Love" singer appeared to remain honest for the majority of the test, at one point, he got caught lying after he shared his initial -- and, apparently, not-so-truthful -- thoughts about Taylor's boyfriend Joe Alwyn.
After Shawn spoke about his friendship with Taylor, with whom he toured back in 2015, the Grammy nominee was asked if he "approves" of Taylor's actor beau.
"I've never personally met Joe, but he looks like a sweet guy," Shawn said, to which the lie detector operator immediately noted, "You're not telling the truth. You're being deceptive."
The musician then got candid, admitting his real thoughts on the "Mary Queen of Scots" star.
"Yeah, I mean, he's kind of got a little bit of a villain look about him," Shawn said. "He looks like a nice guy but, like ... at any, like, movement could turn into a villain, you know?"
"He's got really blue eyes and I struggle with eyes that blue, you know?" he continued. "Like, I find it easier to trust brown eyes." The "Treat You Better" singer then added, "I [just] talked way too much about him."
At another point during the session, Shawn was called out once again for not being honest, however, it wasn't as big of a lie. After weighing in on his pal John Mayer's love life and whether or not he thinks he'll be a "lifelong bachelor" (he doesn't), the "Wonder" singer was asked by the interviewer if he could give John her number.
Shawn said he would "absolutely" pass along her digits -- before the lie detector operator said he was "being deceptive." With a laugh, Shawn admitted, "I was lying."
Meanwhile, Shawn also recalled the first time he met Justin Bieber, whom he's a big fan of and collaborated with on the song "Monster" last year, admitting that he was "definitely" nervous while meeting the singer.
"I think that when I get nervous my face twitches, but apparently it doesn't, but I'm pretty sure I had some face twitching going on," Shawn said of the first meeting. "[I] definitely [said] some weird stuff about how much I love his song 'Smile.'"
The "Mercy" singer was then asked if he spoke to Justin about the 2018 Met Gala, which Shawn attended with Hailey Baldwin, who went on to marry Justin later that year.
"When you met Justin Bieber, did the Met Gala get brought up?" the interview asked while putting a photo of Shawn and Hailey from the event on the table. Shawn responded, "When we met? No, never talked about that."
The lie detector operator then noted that Shawn's answer was honest and that he was "telling the truth."
Also during the test, the "Señorita" crooner was asked if he's ever been "friend-zoned." Shawn admitted that he has been, but "really just a few times by the same girl," before revealing that it was Camila Cabello.
"She's my girlfriend now, so everything's okay," he said with a smile. The couple has been together since July 2019.
Check out more from Shawn's lie detector test -- including whether or not he thinks of himself as a "nice guy" -- in the full clip, above.