NEW YORK — Bryan Cranston is in “deep despair” following the death of his onscreen son, RJ, Mitte, who died by suicide on Monday at the age of 34.

“RJ Mitte, my sweet son on Breaking Bad has died. 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,” Cranston wrote.

“Born with Cerebral Palsy, he never – ever – allowed that challenge to be an excuse for anything,” he continued. “He met the demanding shooting schedule head on with great determination.”

Mitte, who was diagnosed with mild cerebral palsy when he was 3 years old, is best known for playing Walt Jr. on all five seasons of “Breaking Bad.” His character had the same condition as Mitte, who received the SAG-AFTRA Harold Russell Award — given in honor of Russell, the first actor with a disability to win an Oscar — in 2013 for the portrayal.

Cranston also celebrated Mitte’s activism, calling him a “vocal advocate for performers with disabilities.” He noted that Mitte “was the head of a philanthropic organization with a focus on helping the disabled community.”

“It is especially devastating to hear that he took his own life,” he wrote. “Why?”

The “Malcolm in the Middle” actor went on to reveal he’d recently texted with Mitte, and that they tried to make plans to get lunch together, though nothing quite came together.

“I don’t know if that lunch would have changed his future…,” Cranston wrote. “But I do know that I loved him, and thoroughly enjoyed being with him throughout the years on the series, and after the spotlight on Breaking Bad dimmed.”

Cranston concluded: “I’ll miss you son.”

The Emmy winner also encouraged “anyone who is contemplating suicide to please call for the support you need at 988 Suicide & Crisis Lifeline,” adding, “There is hope.”

Fellow “Breaking Bad” actors Dean Norris, who played DEA agent Hank Schrader on the show, and Aaron Paul, who starred as Jesse Pinkman, also paid tribute to their late co-star.

Norris called Mitte’s death “heartbreaking” in a statement shared to social media on Monday.

“Though RJ didn’t play my TV son, I always looked out for him as a young kid on set,” Norris wrote. “He was a sweetheart of a young man and will be greatly missed. This is so heartbreaking, I can’t believe it. Thinking of him and his family.”

Paul, meanwhile, in a statement to the Hollywood Reporter said he was “at a loss” for words upon hearing the news.

“RJ, I love you my friend. You will be missed,” Paul said. “And to whoever happens to be reading this, please know you are loved, and you are not alone. Always remember that.”

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