Gordon's lawyer Joe Habachy confirmed his client's death in a statement on Wednesday. The Atlanta lawyer did not give a cause of death or say where it occurred.

Gordon's death comes nearly five years after Brown, the daughter of singers Whitney Houston and Bobby Brown, was found face-down and unresponsive in a bathtub in January 2015.

The 22-year-old died after six months in a coma.

Investigators with the medical examiner's office were not able to determine exactly how Bobbi Kristina Brown died.

An autopsy showed that she had morphine, cocaine, alcohol and prescription drugs in her body, but the medical examiner couldn't determine if she killed herself, if someone else killed her or if her death was accidental.

Her family blamed Gordon, accusing him in the lawsuit of giving her a "toxic cocktail" before putting her face-down in the water.

Gordon was never charged in the case, but he was found responsible in a wrongful death lawsuit. An Atlanta judge ordered him to pay $US36 million ($A51 million) to Brown's estate.

Houston brought Gordon into her household as an orphan at the age of 12, raising him and her daughter after divorcing Bobby Brown in 2007.

Gordon wore a large tattoo of Houston's face on his arm and called the singer "mom," but the music superstar never fully adopted him or included him in her will.

Houston died in 2012 after she drowned in a bathtub. Coroner's officials ruled Houston's death accidental and said heart disease and cocaine were contributing factors.

After Houston's death, Gordon and Bobbi Kristina went public with their romance.

"Despite all of the incredible challenges Nick faced over the last few years I can honestly say that he worked hard to hold his head up and stay sober and that he genuinely wanted a happy healthy life with his family more than anything else," Habachy said in a statement.

Australian Associated Press