Lou Reed died of liver disease.

The legendary Velvet Underground frontman and pioneer of modern rock passed away on Sunday aged 71, and it has now been confirmed he died of complications with his liver, which he had been suffering with for a year.

The "Perfect Day" star had undergone a liver transplant in April and also had to cancel his Coachella Music and Arts Festival in California due to his illness. The transplant initially appeared to be a success and Lou was looking forward to the future and to returning to performing. "I am a triumph of modern medicine, physics and chemistry. I am bigger and stronger than ever," he wrote on Facebook in June.

However, more recently the singer and guitarist had taken a turn for the worse and when it was confirmed the disease had entered its final stages he refused further treatment and returned home. "We all agreed that we did everything we could," his doctor, Charles Miller, told the New York Times.

Since the highly influential musician passed away, tributes have come flooding in from some of the most respected people in music. "The world has lost a fine songwriter and poet ... I've lost my 'school-yard buddy,'" said his former Velvet Underground bandmate, John Cale.

David Bowie referred to Lou as a "master" while Talking Heads frontman David Byrne said, "His work and that of the Velvets was a big reason I moved to New York and I don't think I'm alone there. We wanted to be in a city that nurtured and fed that kind of talent."