Miller has struggled with substance abuse over the years, most recently getting arrested for DUI and hit and run in May.
Grande at the time wrote on social media that she had long tried to help Miller become sober but described their relationship as "toxic" and said, "I am not a babysitter or a mother and no woman should feel that they need to be".
In the hours after Miller's death was first reported, it emerged that comments had been disabled on Grande's Instagram account, as she had been receiving abusive and upsetting messages from his fans.
"Let's please stop doing that", she continued.
Ariana went on: "Of course I didn't share about how hard or scary it was while it was happening but it was".
"This is one of my best friends in the whole world and favorite people on the planet", Grande wrote of Miller on Instagram after the split. "I respect and adore him endlessly and am grateful to have him in my life in any form, at all times regardless of how our relationship changes or what the universe holds for each of us". Grande and Miller ended their relationship in May.
The photo was left without a caption, meaning the singer continues to stay quiet on the sudden death of her ex-boyfriend.More news: Missouri college drops Nike over new Kaepernick ad campaign
He told Rolling Stone when the album came out: "Have I done drugs?" We made that song and started becoming close again.
Her message was simple: "Rest easy, insane kid".
Ariana and Mac performed together past year at the One Love Manchester concert following the terrorist attack which took place after her concert at Manchester Arena.
The singer shared a sweet picture where the rapper is both looking at her and the sky as he sits on the grass.
Funeral arrangements have yet to be announced, but Miller's loved ones have since released a statement about the tragedy.
They broke up back this past May, with Grande revealing shortly after the breakup that she was seeing Saturday Night Live cast member, Pete Davidson.