Miller, a platinum-selling U.S. musician and the former partner of Grande, was found unresponsive at his home in Los Angeles on Friday, reportedly after an overdose.
Instead of words the No Tears Left To Cry singer shared a simple black and white image of the rapper - who passed away Friday aged 26 from a suspected drug overdose - on Instagram. They performed together at Grande's One Love Manchester concert in May of past year - a benefit for people injured during the terrorist attack on her concert in the city - and were seen together in March at Madonna's Oscar afterparty.
The post has no caption, nor does it particularly need one.
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The star posted a touching pic of Mac on her Instagram account featuring the late rapper sitting down on the ground and looking up at the photographer, presumably Grande.
A source told ET on Friday that Grande was "devastated" by Miller's death. "Ariana is very upset".
Her reaction follows the one of manager Scooter Braun who posted on his own Instagram: 'Always a kind heart.
Toxicology tests have been requested, but Mac's official cause of death can not be confirmed until they come back.
The couple had dated for two years until parting ways in May, shortly before Miller was arrested for driving under the influence (DUI) and hit and run in Los Angeles. According to The Blast, Miller's autopsy was completed by the L.A. County Medical Examiner on Saturday, but the official cause of death was listed as "deferred", pending further tests.Sources claim there was no "obvious" evidence of drug use at the scene, but toxicology tests have been ordered to determine if substance abuse played a part in his passing.