Cameron Boyce's Pal China Anne McClain Breaks Down, No Idea He Had Epilepsy

"Descendants 3" star China Anne McClain grew up with her costar and BFF Cameron Boyce, and says his death hit her like a ton of bricks, because almost no one knew he was suffering from epilepsy.

China was on "TMZ Live" Friday to talk about Cameron and Friday's Disney Channel debut of his final movie, 'D3.' She says the premiere comes with mixed emotions on the heels of her dear friend passing. It was obvious she's still processing the loss.

She says only Cameron's family knew about his condition, and despite the fact she knew him for 10 years -- and starred in 4 movies with him -- she had "no idea."

She broke down as she explained how the simplest things remind her of Cam and sometimes send her on a roller coaster of emotions. China says she's even caught herself picking up the phone to text Cameron.

She says she still hasn't seen "Descendants 3," and confesses she's not sure she'll be able to make it through the whole thing when she finally does watch.

As we reported ... Disney canceled a red carpet event in Cameron's honor after he died last month in his sleep. The studio also made a donation to the Thirst Project ... a nonprofit close to Cameron.