Canadian actor Cory Monteith, 31-year-old heartthrob of Fox's musical comedy television series "Glee", was found dead on Saturday in his Vancouver hotel room, police said.
Police and paramedics found no signs of foul play and the cause of death was not clear, British Columbia Chief Coroner Lisa Lapointe said at a news conference.
Monteith's representatives issued a statement, saying, "We are in shock and mourning this tragic loss" but offering no details on the possible cause of death.
Monteith had talked openly about struggles with substance abuse, and 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.
Asked whether Monteith had died of a drug overdose, Vancouver Police Department Acting Chief Doug LePard said he would "not discuss anything that we might have found in the room at this time."
On "Glee," Monteith played Finn Hudson, a high school football player turned enthusiastic singer in the glee club, or vocal group.
The actor grew up in Victoria, British Columbia and told Parade magazine in 2011 that he had a serious drug problem during his teenage years for which he received treatment. His mother, Ann McGregor, still lives in nearby Victoria.
Other people were in Monteith's Pacific Rim Hotel room on Friday night but evidence, including fob key entries, indicated he returned to his room by himself early on Saturday and was alone when he died, police said. He was due to check out of the hotel later that day.
Vancouver police said Monteith left his hotel with three friends on Friday night, returning alone around 2:15 a.m., the Globe and Mail newspaper reported.
The actor had been dead for several hours when his body was discovered by police and paramedics answering an emergency call.
"The death of a young person is a tragedy for their family, friends and community," Lapointe said. "A sudden death is more shocking and our hearts go out to the family and friends who are mourning the loss of this young man."
An autopsy was set for Monday.
Friends and colleagues expressed shock after having seen Monteith who they said seemed fine in recent weeks.
Adam Shankman, who directed "Glee" episodes, told CNN, "I had several interactions with him yesterday where he said that he was doing amazing. He even said I am feeling fantastic."
"I'm like everybody else, really devastated and confused by what happened," Shankman said.
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."
But "Glee," a show set in the small town of Lima, Ohio, was Monteith's breakthrough. A big part of the show was his character's on-again-off-again romance with glee club star Rachel Berry, an aspiring entertainer played by Lea Michele.
Monteith and Michele followed in the footsteps of their fictional counterparts by dating in real life. They appeared publicly together as recently as last month at a charity ball.
A representative for Michele said she had not issued a statement following Monteith's death.
Dot-Marie Jones, who plays "Glee"'s football coach, said on Twitter, "I have no words! My heart is broken."
In recent episodes of the series, Rachel had left to attend college in New York while Finn stayed in Lima, where he worked at his father's auto repair shop and later got involved in helping lead his former school's glee club.
In a statement on the "Glee" Twitter page, the show's executive producers and Fox said they were "deeply saddened by this tragic news".
"Cory was an exceptional talent and an even more exceptional person," the message said. "He was a true joy to work with and we will all miss him tremendously. Our thoughts and prayers are with his family and loved ones."
(Additional reporting by Piya Sinha-Roy in Los Angeles, Jennifer Kwan in Victoria and Chris Michaud in New York; Editing by Cynthia Osterman)