McCartan, 26, dropped the bombshell during a Q&A on his Instagram Stories on Thursday, answering a fan who asked, “What’s your proudest moment?”
“Within two weeks, my fiancée cheated on and left me,” McCartan alleged without mentioning Cameron, 24, by name.
“I almost died from food poisoning, and Donald Trump was elected president. I truly didn’t think I would be able to make it through that part of my life,” McCartan continued.
Despite his sorrow, McCartan said, “I’m proudest of the light that came from that darkness, and my ability to survive and turn the anger and sadness I had into positive life changes and a new way forward.”
Cameron seemingly responded to the accusations on Twitter by retweeting a quote that reads “When a toxic person can no longer control you, they will try to control how others see you.”
“The misinformation will feel unfair, but stay above it, trusting that other people will eventually see the truth, just like you did,” the tweet concluded.
— Dove Cameron (@DoveCameron) January 17, 2020
Alongside the message, Cameron wrote “Beautiful,” prompting fans to assume her tweet was aimed at McCartan.
Reps for both Cameron and McCartan did not immediately respond to PEOPLE’s request for comment.
Cameron and McCartan split in October 2016 — just six months after getting engaged.
“Dove has decided this relationship isn’t what she wants. We still love each other very much. Please be sensitive, as this is painful,” McCartan tweeted at the time.
The Disney Channel Liv and Maddie costars dated for three years before he popped the question.
“We were both very clear with each other that it was like, ‘I know you’re my person. You know you’re my person. There’s nobody else,’” Cameron told PEOPLE at the 23rd annual Race to Erase MS gala in Beverly Hills in April. “But I knew he wanted to get married young – he had told me that. He was like, ‘That’s what I want as my life plan.’”
But when it came to actually proposing, “he didn’t hint at it,” the actress said. “It was very spur-of-the-moment. It was perfect.”
The duo, who met on the set of Liv and Maddie in 2013, also formed a pop band together in 2015 called The Girl and the Dreamcatcher.
In July 2019, Cameron opened up about their abrupt split explaining to Seventeen that she felt pressured to “make everything look perfect all the time” during her relationship with McCartan.
“It was my first ever real relationship, and it was on-screen and off-screen,” she told the outlet. “A lot of what I went through in that first relationship, the very low-lows, I did not make public.”
“I was under the impression that I had to make everything look perfect all the time and my partner definitely put that in my ear,” she continued. “People thought I was sharing loads, but I hardly shared anything.”
Cameron has since moved on and is now dating actor Thomas Doherty.
“She is just the most incredible person I’ve ever met,” Doherty said to ET. “I think people see her as so talented — because obviously that’s her job, to perform and all the rest of it — but she’s the most compassionate and the most patient and the most genuine, loving person I’ve ever met. And so kind and so generous. She’s amazing. She really is.”
In response, Cameron told Entertainment Tonight, “I cry, like, every day when I’m with him because… he’s just the most pure, loving, selfless, generous, kind . If I’m going to marry anyone, it’s going to be him.”