The actress says she's relying on her co-stars for support.
"When I heard about Cameron, I had just woken up early in a London hotel room to the sound of my phone ringing off the hook," Cameron, 23, recalls. "I was nervous about why I could be getting so many texts and calls, so I only looked at my mother's text. I knew she would be the gentlest, and the most concise, whatever it was."
"It explained what had happened and I immediately phoned Boo Boo [Stewart], who had already called me twice," she adds. "We just sobbed without speaking. If there was a word stronger than devastated that could describe the depth of pain that I was feeling, I would use it."
Even before they worked together on Disney's Descendants franchise, Cameron says she had always wanted to befriend Boyce, whom she knew from his starring role opposite Debby Ryan on Jessie.
"I had always thought, 'Damn, what a charismatic, bright and brilliant kid,'" she remembers, telling the outlet that she gave him a giant hug the day they finally met in person. "This is going to sound so weird, but we're about to do this new thing together, and I'm going to hug you, because I can promise you now, we are going to be friends."
"From that first day onward, Cameron was my friend and he treated me like he treated everyone else; like they were the most important person in the room," she continues. "I loved him like a brother, and I learned from him every day, how to be joyful, how to be resilient, how to be patient, no matter the circumstances. I couldn't begin to quantify the wisdom and generosity that this kid had. I still learn from him every day."
Cameron says that the entire Descendants cast has been supporting each other throughout this tumultuous time.
"Me, Boo Boo, Cam and Sofia [Carson] still have our core 4 group chat active and open, as we have for 5 years," she reveals. "It's hard when there are no adequate words to express the pain we are all feeling, but the usual text is 'love you.' Or 'Are you eating?' Or 'How are we all today?' I think something like this horrible loss makes you realize how important you are all to each other. I am grateful for my chosen family at a time like this."
Earlier this month, ET spoke with Descendants 3 director Kenny Ortega at his Walk of Fame ceremony in Hollywood, where he explained how he plans to carry on Boyce's legacy.
"Everything that Cameron's in, he brings the light. Every room that he walked into, every cause that he pushed for and everything that he ever did, it was impossible not to be drawn into him," Ortega said. "That's how I found him. I fell in love with him when he was doing Jessie, and I went after him for Descendants."
"Descendants 3, you know, again will just remind everybody of his incredible gift," he expressed. "He was bioluminescent. He was lit from the inside out. He really was, and we will miss him, but we will carry his legacy forward."
The third chapter of The Descendants franchise is set to premiere on the Disney Channel on Friday, Aug. 2. Hear more in the video below.