It's been almost exactly a year since Prince died and just out, an update in the investigation into his drug overdose.

FOX's Eben Brown reports:

A physician treating the artist Prince had been prescribing oxycodone to the singer, but had been writing the prescriptions for a patient with the name of one of Prince's friends.

The doctor, Michael Todd Schulenberg, reveals in an affidavit he did this to preserve Prince's privacy.

The investigation has shown Prince had been battling opioid addiction, but that his death, an accidental overdose, was caused not by oxycodone but fentanyl, a drug said to be 50 times as powerful as heroin.

Eben Brown, FOX News.

Follow Eben Brown on Twitter: @FOXEbenBrown