The cause of Lou Reed's death was liver disease, the New York Times reported.

Dr. Charles Miller of the Cleveland Clinic in Ohio - where Reed had liver transplant surgery this past April - said the former Velvet Underground singer was back at the Clinic last week for treatment.

Miller had performed Reed's surgery earlier in the year and said the singer decided to return home after his end-stage liver disease could no longer be treated. "We all agreed that we did everything we could," Miller told the Times.

Read: Lou Reed Dies at 71

Reed died yesterday at his home on Long Island at the age of 71. He was scheduled to perform at the Coachella music festival in April, but had recently cancelled citing "unavoidable complications."

Reed was able to keep his April surgery a secret at the time, but shortly after, his wife Laurie Anderson revealed how serious his condition was to the London Times.

"I don't think he'll ever totally recover from this, but he'll certainly be back to doing [things] in a few months," Anderson told the Times. She also noted that Reed, who's an avid martial arts enthusiast, was 'already working and doing t'ai chi' within a month of the surgery."

In June, Reed posted a message on his Facebook page about his recovery and his hope to return to the stage.

"I am a triumph of modern medicine, physics and chemistry. I am bigger and stronger than stronger than ever," wrote Reed. "I look forward to being on stage performing, and writing more songs to connect with your hearts and spirits and the universe well into the future."