Nelsan Ellis died due to alcohol withdrawal complications,

"True Blood" star Nelsan Ellis' family has revealed that the actor struggled with drug and alcohol abuse for years and the battle ultimately cost his life.
Ellis died Saturday of heart failure. His manager Emily Gerson Saines confirmed the actor's death to The Hollywood Reporter, saying, "Nelsan has passed away after complications with heart failure. He was a great talent, and his words and presence will be forever missed."
A few days after his death, Ellis' family agreed to release a statetment to the American digital and print magazine, through Saines, the exact circumstances around the actor's demise.
"Nelsan has suffered with drug and alcohol abuse for years. After many stints in rehab, Nelsan attempted to withdraw from alcohol on his own.

"According to his father, during his withdrawal from alcohol he had a blood infection, his kidneys shut down, his liver was swollen, his blood pressure plummeted, and his dear sweet heart raced out of control," Saines said.
Ellis played Lafayette Reynolds on "True Blood" from 2008 until the series' completion in 2014. He then went on to star as Bobby Byrd in the 2014 James Brown biopic "Get on Up".