The estate of Bobbi Kristina Brown claimed in an amended lawsuit that her partner, Nick Gordon, gave her a "toxic cocktail" and placed her in a bathtub full of cold water the day she was found unconscious.
The suit was originally filed in June and was amended Friday to add new allegations. The daughter of Whitney Houston and Bobby Brown died July 26, nearly six months after she was found unconscious in a home in Roswell, Georgia.
The lawsuit claims that on the morning of January 31, Gordon came home to Brown, 22, after an all-night "cocaine and drinking binge." The couple argued loudly for about 30 minutes, during which he accused her of cheating, the lawsuit says. Then "everything abruptly became quiet."
The lawsuit alleges Gordon "gave Bobbi Kristina a toxic cocktail rendering her unconscious and then put her face down in a tub of cold water causing her to suffer brain damage."
"Bobbi Kristina was subsequently diagnosed with global and irreversible brain damage and died as a result of Defendant's actions," the lawsuit says.
The Fulton County medical examiner found no obvious cause of death or significant injuries in Brown's initial autopsy. Additional laboratory testing is expected.
The lawsuit also alleges previous abuse by Gordon. It claims that, days before Brown was found unconscious, Gordon hit her in the face, knocked her to the floor, and "continued to beat her in the face until she was bloody."
The lawsuit also claims Gordon stole from Brown's bank account while she was in a coma. Brown's estate is asking for $10 million in punitive damages.
Gordon's legal team, Joe Habachy and Jose Baez, called the lawsuit "slanderous and meritless."
"Nick has been heartbroken and destroyed over the loss of his love and it's shameful that such baseless allegations have been presented publicly," the two said in a statement. "Nick has engaged civil counsel and intends to defend the lawsuit vigorously and expose it for what it is: a fictitious assault against the person who loved Krissy most."
A request for comment from Brown's estate wasn't returned.
The circumstances surrounding Brown's death are still under investigation, according to the Fulton County district attorney.
ABC News' Shahriar Rahmanzadeh contributed to this story.