Update 02/07/2020 1:49am:

According to the autopsy and toxicology report for Nick Gordon, the 30-year-old died of a heroin overdose on New Year's Eve. TMZ reports that Gordon went into cardiac arrest and was hospitalized for seven hours before he passed away. There was apparently Narcan (a substance used to counter the overdose) in Gordon's system at the time of death. 

It was also reported by emergency personnel that Gordon's brother found him foaming at the mouth with a blackish discharge. This is consistent with most heroin overdoses.

Original 01/01/2020 7:07pm:

According to the Daily Mail, the late Bobbi Kristina Brown's controversial ex-fiancé, Nick Gordon, has reportedly died of an apparent drug overdose. The 30-year-old Gordon was rushed to the hospital after a New Year's Eve celebration with doctors informing his family early New Year's Day that they were unable to revive him. Gordon's brother, Junior Walker, confirmed the news on Facebook as he wrote: "God why did I have to lose my brother on New Year," and "All I can do is cry." 

Source: dailymail.co.uk