Former New England Patriots star Aaron Hernandez killed himself in his prison cell last April as he served a life sentence for a 2013 murder charge at the Souza-Baranowski Correctional Center in Shirley, MA.

His lawyers revealed today that tests on Hernandez’s brain “showed severe signs of the degenerative brain disease chronic traumatic encephalopathy (CTE).” They also said that his daughter plans to sue the NFL and the Patriots “for leading Hernandez to believe the sport was safe.”

From Sports Illustrated:

Hernandez’s brain, which was donated after his death, was examined by Dr. Ann McKee at Boston University. Dr. McKee diagnosed Herandez with Stage 3 CTE (out of four) and released images of his brain which show early brain atrophy and “severe deposition” of the protein associated with CTE. The disease is believed to be caused by repeated blows to the head, which is why it often affects football players, hockey players and boxers.

Stage III CTE is “usually seen in players with a median age of death of 67,” Hernandez’s lawyers wrote in a lawsuit filed Thursday.

According to Baez, Hernandez’s CTE “was the most severe case they had ever seen for someone of Aaron’s age.”

ESPN explained that repeated trauma can cause CTE, which exhibits “symptoms such as violent mood swings, depression and other cognitive difficulties.” Unfortunately, doctors can only diagnose CTE in an autopsy.

The lawsuit was filed today:

The $20 million lawsuit filed in federal court in Boston on Thursday claims that the team and league deprived Avielle Hernandez of the companionship of her father. It is separate from a $1 billion settlement in which the league agreed to pay families of players who suffered brain damage because of repeated head trauma while playing football.

An NFL spokesman said, “We have not seen a copy of the suit and cannot comment at this time.”

The New York Times reported that if anyone under the age of 45 had CTE they “can receive as much as $4 million” and those players “who died after the settlement was approved in April 2015 are not eligible for an award, but Hernandez’s family could argue for an exemption.”

Hernandez is not the only who doctors found with CTE:

Hernandez is the latest former N.F.L. player to have committed suicide and then been found with C.T.E., or chronic traumatic encephalopathy, joining Dave Duerson, Junior Seau, Andre Waters, Ray Easterling and Jovan Belcher, among others. Seau and Duerson deliberately shot themselves in the chest so that researchers would be able to examine their brains. Hernandez was found hanging in his prison cell.

Seau, Duerson and Waters were all older than 40, making him one of the youngest former N.F.L. players to have been found with C.T.E. In July, researchers at Boston University released findings that showed that they had found C.T.E. in the brains of 110 of the 111 former N.F.L. players they had examined.