Miller, real name Malcolm McCormick, was found dead after suffering an apparent overdose on 7 September, and now, seven days later, the "No Tears Left to Cry" singer, who dated the late rapper for almost two years before they broke up in May, has broken her silence about the tragedy.
Sharing old video footage of a smiling and laughing Mac telling her a story over dinner, she added a moving caption, which read: "i adored you from the day i met you when i was nineteen and i always will. i can't believe you aren't here anymore. i really can't wrap my head around it."
Mac's friend Shane Powers came forward earlier this week to defend Ariana from online trolls, who accused her of causing the "Self Care" rapper's death, and insisted that Grande was really instrumental in supporting the hip-hop star's sobriety battle while they were together.
Ariana pointed out how much energy she invested in helping to get her boyfriend sober as she continued with her heartbroken message.
"we talked about this. so many times," she added. "i'm so mad, i'm so sad i don't know what to do. you were my dearest friend. for so long. above anything else."
"i'm so sorry i couldn't fix or take your pain away. i really wanted to. the kindest, sweetest soul with demons he never deserved. i hope you're okay now. rest."
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i adored you from the day i met you when i was nineteen and i always will. i can’t believe you aren’t here anymore. i really can’t wrap my head around it. we talked about this. so many times. i’m so mad, i’m so sad i don’t know what to do. you were my dearest friend. for so long. above anything else. i’m so sorry i couldn’t fix or take your pain away. i really wanted to. the kindest, sweetest soul with demons he never deserved. i hope you’re okay now. rest.
Ariana, who is now engaged to comedian Pete Davidson, is the latest star to pay tribute to her ex - Kendrick Lamar, J. Cole, Charlie Puth, Chance The Rapper, Kehlani and countless others have also shared their grief, while Ariana's brother Frankie Grande opened up about the heartbreak he felt surrounding his friend's death in a lengthy social media tribute earlier this week.
Mac was also honoured in his native Pittsburgh, Pennsylvania on Tuesday night, as hundreds of fans gathered for a candlelight vigil led by his grandmother Marcia Weiss.
Mac will reportedly be laid to rest in a Pittsburgh chapel in the coming days.