John Mayer was so upset about Mac Miller's death because he "didn't" know him well.

John Mayer

John Mayer

The 'Free Fallin' hitmaker was devastated when the rapper died from an accidental drug overdose in September but admits what hurt him about his passing the most was that he didn't know him well and he only "wishes he had more to tell" people about Mac.

Alongside a picture of Mac, he wrote on Instagram: "Several weeks ago, I was sent an email asking if I wanted to take part in a Mac Miller tribute for a magazine as part of an end-of-year recap. I passed on it, not because I didn't want to talk more about him, but because I couldn't; I had shared all the memories I had of him in the brief time of our getting to know one another. I replied to the email and sat in silence for a few minutes. That day, I discovered a new dimension to the sadness of his passing - I wasn't upset because I knew him well. I was upset because I didn't. I wish I had more to tell you about Mac Miller. What I do have to remember him by are a couple of beautiful mental photographs that I'll keep with me the rest of my life."

Last month, Mac's death was ruled an accident, with the Los Angeles County Department of Medical Examiner-Coroner saying his passing was due to mixed drug toxicity of fentanyl, cocaine and alcohol. Though the amount of each substance wasn't necessarily lethal, it was the combination of drugs that proved fatal.