Prince’s addiction to opioid painkillers, which has come to light since his death, was hidden from even some of his closest friends, The New York Times reports.

Prince had a reputation for leading a clean lifestyle, avoiding alcohol and marijuana and eating a vegan diet. While many people close to him say they never saw Prince take any pills, evidence is mounting that he had become dependent on painkillers, according to the newspaper.

His dependence on pain pills became so great that friends called Dr. Howard Kornfeld, a California specialist who treats people addicted to pain medication. Dr. Kornfeld sent his son Andrew to meet with Prince at his Minnesota home, but he arrived too late, according to William J. Mauzy, an attorney for the Kornfeld family.

In April, Prince’s private jet made an emergency landing in Moline, Illinois after he became unresponsive. City records show emergency responders rushed him to the hospital, where he was treated with a shot of the opioid overdose drug Narcan (naloxone). He stayed in the hospital for a few hours and flew back home.

His publicist later said Prince had the flu, but his friends became concerned and decided they might need to seek help from an addiction specialist.

Prince suffered hip pain after decades of strenuous performances, the article notes. He regularly jumped onstage in platform heels. He began taking painkillers for his hip pain years ago, and had hip surgery in the mid-2000s. He was then prescribed more pain medicine, according to an anonymous person who worked with Prince.

On Wednesday, officials with the Drug Enforcement Administration and the United States Attorney’s Office announced they were joining the investigation into Prince’s death.

Photograph: NPG Records