The British Columbia Coroners Service said in a release that post-mortem testing on the star, who was found dead on Saturday in a downtown Vancouver hotel room, died of “a mixed-drug toxicity involving heroin and alcohol.” It said Monteith’s death was unlikely to have been intentional.

“There is absolutely nothing at this point, no evidence to suggest this is anything but the most sad and tragic accident,” said Barb McLintock, a spokeswoman for the Coroners Service.

Monteith was found dead shortly after noon on Saturday in his room at the Fairmont Pacific Rim hotel. Vancouver police said they believed he was alone in the room after returning to the hotel early on Saturday morning.

Representatives for the actor’s girlfriend, Lea Michele, who played Monteith’s on-screen love interest in “Glee,” issued a statement on Tuesday thanking fans for their support.

“Since Cory’s passing, Lea has been grieving alongside his family and making appropriate arrangements with them,” Michele’s representatives said in a statement. “They are supporting each other as they endure this profound loss together.”

Monteith was public about his struggles with substance abuse. In April, he completed voluntary treatment for unspecified substance addiction at a rehab facility. He had also been treated in a facility at age 19.

“GLEE” WAS BREAKTHROUGH

The actor, who was born in Calgary, Alberta, and grew up in Victoria, British Columbia, told Parade magazine in 2011 that he had a serious drug problem during his teenage years for which he received treatment.

Monteith is the latest prominent young entertainment star to have died from drugs or alcohol. British soul singer Amy Winehouse died in 2011 from accidental alcohol poisoning at the age of 27.

Other notable recent drug-related deaths in Hollywood include Oscar-winning Australian actor Heath Ledger, who died in 2008 from an accidental overdose of prescription drugs at age 28, and former child star Brad Renfro, who died from an accidental heroin overdose a week before Ledger at age 25.

Monteith began his career in a number of small roles leading up to a recurring part between 2006 and 2007 in the ABC Family science-fiction drama “Kyle XY” and another role around the same time on the MTV series “Kaya.”

“Glee,” which is set in the small town of Lima, Ohio, was Monteith’s breakthrough. It is centered on a high school glee club. Popular for its song and dance routines and big-name guest stars, the show has won Golden Globe, Emmy and Peabody awards.

Monteith’s death is a major blow to a show that promotes a positive message, and his character, high school athlete Finn Hudson, who grew to defend the school’s misfits, played an integral part in advancing the series’ theme of tolerance.

The fifth season of “Glee” is expected to premiere on Sept. 19 on U.S. broadcaster Fox, which is owned by Twenty-First Century Fox Inc. DM

Photo: Actor Cory Monteith arrives at the “Do Something Awards” in Santa Monica, California August 19, 2012. REUTERS/Gus Ruelas