The lawsuit filed Friday alleges Nick Gordon, who shared a townhome with Brown in the Atlanta suburb of Roswell, beat her after an argument on the morning of January 31, then gave her a "toxic cocktail" to knock her out.
It accuses him of placing her face-down in a bathtub of cold water, causing her to suffer brain damage.
The suit seeks at least $10 million.
Gordon has never been charged in relation to Brown's death, and his legal team says the suit is "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," Joe Habachy and Jose Baez 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."
Speculation about Brown's injuries began soon after she was hospitalized. Daphne Barak, a friend of Brown, said in February
that police had questioned Gordon about bruises on Brown's chest. Barak said Gordon told her they were a result of him performing CPR.
Gordon was not allowed to visit Brown in the hospital, and he did not attend her funeral
Lawsuit alleges previous abuse
The lawsuit was filed in Fulton County Superior Court in Atlanta by Bedelia Hargrove, the administrator of Brown's estate.
It claims Gordon controlled Brown's interactions and manipulated her bank accounts so he could access her money, "routinely transferring a large portion" of her funds into his accounts without Brown's consent or authorization.
It also says he installed cameras throughout their townhome so he could watch and hear her.
"This was all part of a scheme to control Bobbi Kristina and benefit from her wealth," the suit states.
It describes previous instances of alleged physical abuse, including one incident days before her near-drowning on January 31.
Witnesses were present, the lawsuit alleges, when Gordon lunged at Brown on the living room couch so hard that the couch broke and she was knocked to the floor. He continued to beat her in the face until she was bloody and then kicked her in the side until she was screaming and curled up on the floor, the suit says.
The attack caused Brown to lose a tooth and blood was on the floor, the suit says.
"Defendant then demanded that she go upstairs," the lawsuit reads. "Bobbi Kristina began crawling on the floor because she could not stand up due to the injuries Defendant inflicted.
"Defendant then dragged her upstairs by her hair and threw her in the master bedroom, leaving blood on the walls of the staircase. Afterward, Defendant stated to persons present, 'I don't do this often,' indicating this was not the first time Defendant beat her."
The day she was hospitalized
Shortly before January 31, Brown confided in someone that Gordon "was not the man she thought he was," and she scheduled a time to meet that person, the suit says. The meeting never took place.
About 6 a.m. on January 31, Gordon returned from an all-night "cocaine and drinking binge," the lawsuit states. He reviewed surveillance camera footage and listened to Brown's conversations, which led to an argument that began in the kitchen, moved to the living room and ended upstairs in the master bedroom.
The argument lasted about 30 minutes, it says.
"Upon information and belief, Defendant 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," the lawsuit reads. He then got in bed with a female guest, it says.
About 15 minutes later, someone in the townhome went to check on Brown and found her face down in the bathtub, unresponsive and unconscious, her mouth swollen and a tooth hanging loosely from her mouth, the suit says.
"When the Defendant came into the master bedroom, the very first thing Defendant did was let the cold water out of the bathtub and later shouted, 'Clean up, clean up.' Others began mouth to mouth resuscitation to no avail. Defendant then began to slap her saying, 'wake up,' and also started performing CPR between slaps."
Evidence or allegations?
The lawsuit doesn't explain whether there is evidence to back up the allegations.
It's possible that some of the incidents were captured on the surveillance system and obtained by investigators or the family, but that's not clear. It's also possible that the unnamed people mentioned as being present during the alleged incidents shared some information.
Regardless, Georgia law requires attorneys to have some evidence that leads them to believe a claim is true, says CNN legal analyst Philip Holloway
"Before a lawyer can make an allegation in a lawsuit, the lawyer must have a good-faith basis for making the claim," Holloway said. "In all likelihood the plaintiffs' attorneys are aware of some of the evidence uncovered by law enforcement, but they may have been doing their own investigation simultaneously."
No cause of death released
The initial portion of Brown's autopsy
did not show an "obvious underlying cause of death" and noted no significant injuries, the Fulton County Medical Examiner said. But it noted the long passage of time between the January 31 incident and Brown's death will make it difficult to determine what happened.
"We do not plan to complete the death certificate or determine a cause and manner of death until all test results are completed and all investigative, medical and other documentary records are received and thoroughly reviewed," the medical examiner said in a statement.
Brown was buried Monday in New Jersey, next to her mother.