Bryan Cranston has paid tribute to his Breaking Bad co-star RJ Mitte, who played his on-screen son Walter White Jr. in the acclaimed crime drama, following the actor’s death at 34.

Cranston shared an emotional message on Instagram after news of Mitte’s death emerged on October 12. “I’m in deep despair as I write this tonight. RJ Mitte, my sweet son on Breaking Bad has died,” the actor wrote, recalling how he first met Mitte when the latter was just 14 and had been cast as Walter White Jr., also known as Flynn, in the AMC series.

“I’m in deep despair as I write this tonight. RJ Mitte, my sweet son on Breaking Bad has died,” Cranston wrote. He recalled first meeting Mitte when the actor was 14 and reflecting on his growth throughout the series, which ran from 2008 to 2013.

Cranston also praised Mitte’s determination and his work advocating for greater representation of people with disabilities in the entertainment industry. Mitte, who had cerebral palsy, built a career spanning television and film while using his platform to promote disability awareness and inclusion.

“All that promise and potential now is such a loss,” Cranston wrote, expressing his grief over the loss of his former co-star.

The actor revealed that he and Mitte had exchanged text messages just weeks before his death while trying to arrange lunch. Cranston expressed regret that they had not managed to meet and concluded his tribute with the words, “I’ll miss you, son.”

Cranston also encouraged anyone experiencing suicidal thoughts to seek support, sharing the number for the 988 Suicide & Crisis Lifeline in the United States.

Mitte played Walter White Jr., the son of Cranston’s Walter White and Anna Gunn’s Skyler White, throughout all five seasons of Breaking Bad. His other acting credits include the television series Switched at Birth, The Guardians of Justice and the film Triumph. Beyond acting, he became an advocate for disability representation and greater opportunities for performers with disabilities.

Other Breaking Bad cast members also remembered Mitte following news of his death. Aaron Paul, who played Jesse Pinkman, expressed his affection for the actor, while Dean Norris described him as “a sweetheart of a young man” and said he was heartbroken by the news.