According to Michael Clarke Duncan's newly-released death certificate, the actor died of respiratory failure.

On Monday, friends and family attended a special service in Los Angeles for "The Green Mile" star, and new details about his Sept. 3 death have surfaced weeks after he had a heart attack at his home.

According to TMZ.com, one of the contributing factors to his death was severe lack of oxygen to his brain. Other underlying causes were an irregular heartbeat and acute myocardial infarction.

Duncan starred in films such as "Armageddon," "The Whole Nine Yards," and "Green Lantern." He was just 54 years old when he passed away.