Kovar, 29, had long battled addictions to drugs and alcohol, but a cause of his death has not been disclosed.
He was found unresponsive and bleeding from the nose and ears Friday morning at the home of Stacey Achterhof, a female friend who lives near Chicago.
Achterhof called 911, but paramedics were unable to revive him and declared him dead at the scene.
TMZ cited law enforcement sources as saying they suspect he suffered an aneurysm after taking a lethal combination of drugs, but an official cause of death will not be determined until toxicology test results are reviewed.
There is no indication at this time Achterhof will be charged with any crime, TMZ said.