RJ Mitte -- who played Walter White Jr. on "Breaking Bad" -- is dead ... TMZ has learned.

A county official confirmed to TMZ that RJ died Monday in Texas. We're told he died by suicide.

Law enforcement tells us the death investigation is ongoing.

Earlier this month, RJ hung out with his 'Breaking Bad' costar Luis Moncada and they looked to be in good spirits ... they were all smiles in social media posts.

RJ appeared in 56 episodes of "Breaking Bad" ... and he's also known for his work in "The Oak Room," "The Recall," and "The Guardians of Justice (Will Save You!)."

He was engaged to Kennedy Suarez ... he popped the question last year after years of dating.

The last time we got RJ was in 2019, when he talked to our photog about disabled actors needing more representation in Hollywood.

RJ was 34.

RIP

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