Scott Thorson -- Liberace's one-time boyfriend who was portrayed by Matt Damon in "Behind the Candelabra" -- is back in jail because of a dirty drug test .... TMZ has learned.
Law enforcement sources tell us Thorson was popped for violating probation... after he FAILED a random drug test. Sources close to Scott tell TMZ he tested positive for meth ... a drug he's struggled with for years.
FYI -- Thorson had recently gotten out of the slammer for a burglary and identity theft conviction.
Thorson suffers from stage II colon cancer. Dennis Hof -- who runs the famous Bunny Ranch brothel in Nevada -- has been helping Thorson and even got him out of jail recently so he could get proper medical treatment.
BUSTED FOR METH
9/6/2013 12:53 PM PDT BY TMZ STAFF
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