Prince died a day before appointment with opioid specialist

It's been over two weeks since the iconic music sensation Prince was found dead in his house in Minnesota. Millions of his fans continue to mourn the great loss as investigations are still in progress to ascertain cause of the singer's death.

Prince's lawyer has now made it public that the pioneering pop singer was scheduled to see a doctor who specialises in treating opioid addiction at Paisely Park complex on April 22.

However, it was later proved that the appointment should have been taken for an earlier date as the pioneering singer departed for his final abode a day before.

At a press conference, Prince's lawyer William Mauzy told reporters that the singer's representatives had on April 20 contacted California's Dr. Kornfeld for providing medical help to the singer.

Mauzy said: "Dr. Kornfeld felt that his mission was a life-saving mission."

The news came shortly before federal authorities, including the Drug Enforcement Administration, announced they were joining the investigation into Prince's death.

What led to the singer's death still remains undetermined and the autopsy results could still take weeks to come out. Police have said they found no signs of suicide or obvious trauma.

Kornfeld runs a clinic in Mill Valley called ‘Recovery Without Walls' and he planned to fly to Minnesota to meet with Prince on April 22, Mauzy said. In the meantime, his son, Andrew Kornfeld, a staff member at his clinic, traveled to Minnesota on April 21 for an initial discussion.

Mauzy said when Andrew Kornfeld arrived at Paisley Park, the home-studio complex Prince owned in a Minneapolis suburb, the singer was not available. A staff member found the artist unconscious in an elevator, and Kornfeld called 911.

Mauzy confirmed Andrew Kornfeld had opioid medication used to treat pain and addiction in his backpack, but emphasised that no drugs were given to Prince by the doctor or his son.

It was not immediately clear whether Kornfeld's drugs were the same medication the law enforcement source said was found at the scene.

In a statement, the US Attorney's office in Minnesota said it would join the Carver County Sheriff's ongoing probe into Prince's death.

"The DEA and US Attorney's office are able to augment this local investigation with federal resources and expertise about prescription drug diversion," the office said.

Mauzy expressed concern that Andrew Kornfeld could face charges, but said he believes he would have immunity with regard to the medication in his backpack under a Good Samaritan 911 law. The lawyer did not elaborate further on possible charges.

Andrew Kornfeld was interviewed by investigators from the sheriff's office on April 21 and returned to California that night, Mauzy said.

Howard Kornfeld's clinic specialises in medical treatment for chronic pain and drug and alcohol addiction, according to its website.

"Dr. Kornfeld was never able to meet Prince, never talked to Prince, and was sadly not able to arrive in time to help Prince," Mauzy said.

Representatives for the late singer did not immediately respond to a request for comment.