Mendes, who was sporting longer hair, told host Jimmy Fallon on Tuesday that he has been staying with Cabello in Miami during the COVID-19 pandemic and that the experience has given him peace of mind.
"There was a real place inside of me that was scared of saying something wrong or doing something wrong or like saying the wrong thing. And I think that after kind of chilling out and reflecting a bit, I found this place where I realized when we're talking about matters of the heart, you don't have to be an expert," the singer said.
"The whole album became about this freedom, this like thing of not being afraid of talking about things that you morally know are right or wrong. And it allowed me to just open up and that's what the whole video looks like. That's what the artwork looks like. That's what the music sounds like. It's internal freedom," he continued.
Mendes said his 17-year-old sister Aaliyah helped him find inspiration for Wonder, while Cabello was there to support and help him with crafting the album.
"From the very beginning I told her my thesis statement of what I wanted the album to be. And it was the best thing I did because there's always a point halfway through a project where you're like, 'This is garbage. This is the worst thing I've ever done. It doesn't sound good. I don't know what I'm doing,"" Mendes said.
"And that's when you need that support to be like, 'No. Stick with the idea because the idea is beautiful and it's gonna turn out.' I probably would've been discouraged enough to like move into a different world sonically if I didn't have her kind of backing me the whole time. So, I'm thankful for that," he continued.
Wonder is set to be released on Dec. 4. Mendes will also be releasing a Netflix documentary titled Shawn Mendes: In Wonder on Nov. 23 that explores his rise to fame, 2019 tour and the making of the album.
The 22-year-old also performed a medley of the songs "Intro" and the title track from Wonder on The Tonight Show. Mendes started by playing the piano during the cinematic performance and then later joined a band onstage.