A source tells PEOPLE that after more than two years together, the pop stars' bond simply couldn't stand the test of time.
"It just wasn't a relationship that can move forward at this point," the insider says. "It seems the romance just fizzled."
Mendes, 23, and Cabello, 24, announced their break-up on Wednesday in a joint statement shared to their respective Instagram Stories.
"Hey guys, we've decided to end our romantic relationship but our love for one another as humans is stronger than ever ❤️" the statement said. "We started our relationship as best friends and will continue to be best friends."
John Shearer/Getty Camila Cabello and Shawn Mendes
"We so appreciate your support from the beginning and moving forward ❤️❤️❤️ Camila and Shawn," the statement concluded.
The longtime friends started dating in 2019, and often shared very public moments of PDA, be it romantic walks through their neighborhood or intimate videos posted to social media.
They spent the COVID-19 lockdown together in Miami, quality time that Mendes said brought them closer together.
"Camila and I were so lucky because we were able to just kind of be in a still moment, and it was the first time in the past six years that we've been just able to relax and not work at all," he told Audacy Check In in August. "We were going on bike rides around Miami, and it just felt really beautiful."
The "Wonder" singer even told PEOPLE last December that he was "counting down the minutes" until he could bring Cabello home to Canada to spend the holidays with his family.
"I don't know why, but I just know that she is," Mendes said of why Cabello was "his person." "I think that your person really just has to be your best friend, and she has been that for so many years now. She is so unapologetically diving into love, and she really taught me what it is to be vulnerable and honest and true in a relationship."
"She's really so brave and courageous in love," he added. "I'm constantly learning from her."
"I probably have a nurturing attitude because I also like being nurtured," the "Havana" singer said. "I'm lucky that my partner is the same way."