Ariana Grande's brother has poured out his heart over his sister's tragic ex-boyfriend Mac Miller, revealing the rapper's death has left him "beyond heartbroken".

Frankie Grande was particularly upset by Miller's suspected drug overdose drama, because he has battled substance abuse himself.

Referring to him by his birth name, Malcolm McCormick, Frankie has taken to Instagram to offer up his tribute to the 26-year-old rapper, calling him "a good friend" and insisting he "was wonderful to my sister".

"He was the reason I went to the rehabilitation center where I was detoxed safely from all of the drugs alcohol and medications I was taking, when I couldn't imagine living without them," Grande writes on Instagram. "It was the place where I found the community of support that showed me that living life without drugs was a possibility and I would never have discovered that if it weren't for Malcolm."

Frankie signs off by thanking Miller "from the bottom of my heart" for always being there for him.

"I remember when I would get 30, 60, 90 days clean and Malcolm would be there with a gift and a card and words of encouragement... telling me that he knew how hard getting sober is and how impressed he was that I was succeeding," the TV personality adds.

"Addiction is a TERRIBLE disease... many people are suffering from addiction like I am and many many of them are losing. Those of us who are struggling with addiction must stay strong. We must continue to work HARD on ourselves every single day and help each other... Malcolm my friend, you will be dearly missed. And I know you will be looking down on me from heaven, proud AF (as f**k) for every day I live my life clean and sober... 453 days and counting."

Miller was found dead at his home in California on Friday (07Sep18). Reports suggest his remains are on their way back to his native Pittsburgh, Pennsylvania, where fans staged a vigil for him on Tuesday night.