They were playing Usher's hit, "Bad Girl" from his blockbuster "Confessions" album ... on which Aaron played drums.
Aaron's wife announced his death Monday, and Ariana was quick to comment on the post ... and leave a similar response on her IG story.
Ariana says ... "I can't wrap my head around this. We were all so incredibly lucky to know Aaron. The absolute brightest light of a human being. Always the kindest, always smiling, I am so honored and thankful our paths crossed and to have spent so much very special time together."
Aaron's family hasn't announced a cause of death.
Ariana's post makes it clear how much he meant to those who knew him and worked with him -- "Thank you for your utter brilliance, for our laughs, and for your kindness always. I will miss your hugs. You are so, so loved and will be so very missed."
Aaron was 47.
RIP
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