Dr. Richard Tooker, chief medical examiner for Kalamazoo County, told the Kalamazoo Gazette in Tuesday’s editions that Hatfield’s death was triggered by acute cocaine intoxication.

Hatfield, 63, died Nov. 5 just hours before a Righteous Brothers concert. He and his partner, Bill Medley, had hits like “Unchained Melody” and “You’ve Lost That Lovin’ Feeling.”

“This is a shock to me,” Medley told The Orange County Register from his home in Newport Beach, California. “I never saw him (use cocaine). I knew absolutely nothing about it. If I had known, I would have said something to him.”

An initial autopsy found Hatfield had advanced coronary disease. A heart attack due to the disease was listed on Hatfield’s death certificate.

However, Tooker said a final cause of death was not determined until after toxicology reports were completed. The death certificate will be changed to reflect cocaine as the cause of death, he said.

Tooker’s office received the report of cocaine intoxication on December 24, but he asked for the information to be released after the holidays out of respect to Hatfield’s family.

Messages left Tuesday with Tooker and the William Morris Agency, which represents the Righteous Brothers, were not returned.