Prince’s family are suing the rock star’s doctor, saying he failed to treat the singer’s addiction to pain medication.
They are accusing Dr Michael Schulenberg of failing treat the star for opiate addiction, and therefore bearing responsibility for his overdose.
Prince was found dead at his Paisley Park estate near Minneapolis on 21 April 2016.
A report by the Midwest Medical Examiner’s Office says the 57-year-old died of an accidental overdose of the drug fentanyl.
Authorities say Dr Schulenberg admitted prescribing oxycodone, a powerful opiate, to Prince through the name of the star’s bodyguard to protect Prince’s privacy, though Dr Schulenberg has disputed that.
The lawsuit claims that the doctor and other defendants had missed opportunities in the weeks before Prince’s death to diagnose his addiction.
They are seeking unspecified damages in excess of $50,000 (£38,000).
Dr Schulenberg’s lawyer said his team believes the lawsuit has no merit.
“We understand this situation has been difficult on everyone close to Mr. Nelson and his fans across the globe,” lawyer Paul Peterson said in a statement.
“Be that as it may, Dr Schulenberg stands behind the care that Mr Nelson [Prince] received. We intend to defend this case.”