US actor RJ Mitte, best known for playing Walter White Jr in the hit drama series Breaking Bad, has died aged 34.

His representative confirmed his death to the BBC, describing him as a beloved actor, philanthropist and disability rights advocate. He was declared dead on 12 October in Brownsville, Texas. The cause of death has not been determined, and an investigation is ongoing. Police do not suspect foul play.

Mitte, who had cerebral palsy, drew on his own experiences to portray Walter White Jr, the son of Bryan Cranston’s character in the Emmy-winning series. He won a Screen Actors Guild Award in 2014 as part of the show’s ensemble cast.

Beyond acting, Mitte advocated for disability awareness and inclusion, serving as an ambassador for United Cerebral Palsy and Shriners Children’s. He also established The Mitte Foundation to support philanthropic and community initiatives, according to BBC.

Cranston paid tribute to his on-screen son on Instagram, saying he was in “deep despair” over the news. “I’ll miss you, son,” he wrote.

Aaron Paul, who played Jesse Pinkman, described himself as heartbroken, while Dean Norris, who played Hank Schrader, remembered Mitte as “a sweetheart of a young man”.

Breaking Bad aired for five seasons from 2008 to 2013, earning 16 Primetime Emmy Awards from 58 nominations. Mitte’s other screen credits include Hannah Montana, Switched at Birth and Talking to Strangers.