Breaking Bad aired on US cable broadcaster AMC for five seasons from 2008-13.
Cranston posted a tribute to his on-screen son on Instagram, writing that he was in “deep despair” following news of Mitte’s death.
The anti-hero drama created by Vince Gilligan earned a whopping 58 Primetime Emmy nominations and won 16, including two for Outstanding Drama Series in 2013 and 2014.
Cranston plays a high school chemistry teacher in New Mexico who turns to a life of crime to support his family after a cancer diagnosis. As he descends deeper into the underbelly of the meth trade, he drifts further from his son, Walt Jr, who makes his displeasure known with levity through much of the series.
“I met him when he was only 14 years old when he was cast as Walter White Jr., a part he played with such joy and enthusiasm,” said Cranston.
“That kid was pretty raw when we started shooting the pilot in February of 2007, but little by little we watched him grow into a really fine actor.”
Cranston wrote of Mitte’s advocacy for performers with disabilities, and noted that he never allowed his cerebral palsy to “be an excuse for anything”.
“All that promise and potential now is such a loss,” wrote the actor, adding that he “thoroughly enjoyed being with him throughout the years on the series, and after the spotlight on Breaking Bad dimmed”.
“I’ll miss you, son,” he said.
In a statement shared with the Hollywood Reporter, Aaron Paul, who played one of the show’s lead characters, Jesse Pinkman, said he was at a loss and heartbroken.
“RJ, I love you my friend. You will be missed,” he said. “And to whoever happens to be reading this, please know you are loved, and you are not alone. Always remember that.”
Dean Norris, who played Mitte’s uncle, Hank Schrader, posted that although “RJ didn’t play my TV son, I always looked out for him as a young kid on set”.
“He was a sweetheart of a young man and will be greatly missed,” Norris wrote.