The cause of his death, which comes just five months after Murphy died at the age of 32, was unknown, the newspaper said.
"We have detectives at scene," Sgt. Louie Lozano told the Times. "They are conducting their investigation. Once we have further information, we will provide it."
Fire Department personnel provided medical services to Monjack, but he was pronounced dead, according to a Los Angeles police sergeant, who declined to give his name to the Times, at the Hollywood Station late Sunday night.
In March, Monjack was moved to set the record straight on rumors about his relationship with Murphy in an interview with Access Hollywood’s Shaun Robinson.
“You told the New York Post you first fell in love with Brittany when she was a teen during a photo shoot. You said, ‘I was very patient.’ What did you mean by that?” Robinson asked.
“I mean, she was like very young. When she was 17, it would’ve been like dating a 12-year-old,” Monjack explained, dismissing the notion that some might call it inappropriate. “There was only eight years between us. It was more of just an attraction to the person.”
As a photographer, he often staged elaborate photo shoots with her. But he hit back at rumors that the two got married in 2007 because the British-born Monjack’s visa was about to expire and he was facing deportation.
“Brittany Murphy marrying for a visa – it’s so crazy," he said.
He also said suggestions that Murphy’s death and the death of Corey Haim were similar were "absurd," saying they made him "furious."
“Corey was someone that had openly used drugs for many, many years and had a problem,” he continued. “Brittany was someone that never used a drug in her life.”
While prescription medications were found in Murphy’s system at the time of her death, Monjack insisted she never abused prescription drugs.