US officials investigating the death of Prince say they want to interview a doctor and his son about a prescription drug taken to the singer before he was found dead last month.
Police in California say they want to know if the two men had a longer term medical relationship with Prince.
They say neither is accused of wrong-doing.
Doctor Howard Kornfeld, who specialises in addiction to painkillers has confirmed that he arranged to treat Prince hours before he died.
However, he was unable to travel at the time and sent his son Andrew, a medical student, to the singer's Minnesota home.
The doctor's lawyer, William Mauzy, said Prince's team had contacted him on April 20th, the day before Prince died.
It was Andrew Kornfeld who made the 911 call after staff found the singer unconscious in an elevator in his Paisley Park compound.
Mauzy said the elder Kornfeld had asked a local doctor to see Prince the following morning. But Prince did not show up to the appointment, he said.
