Nick Gordon had some sort of black fluid foaming out of his mouth when someone called 911 ... and he wasn't breathing.
TMZ has obtained the Florida dispatch audio and it raises questions about the cause of death.
The 911 call came in as "cardiac respiratory" on New Year's Day. As we reported, Nick was rushed to the hospital where he died.
A man claiming to be Nick's brother said Nick died of an apparent OD, and the "black stuff" could support that conclusion. Black discharge is sometimes related to a "foam cone" that comes out of the mouth and nostrils after an opioid OD.
The medical examiner will conduct an autopsy -- possibly Thursday -- and the toxicology results should be available in about 3 weeks.
TMZ broke the story ... Nick was present when Whitney Houston's daughter and his girlfriend -- Bobbi Kristina -- OD'd in a bathtub in 2015. He was found civilly liable for her death and the cops investigated him in connection with her death for years, but he was never charged, and the investigation was still ongoing when he died.