The late Aaron Hernandez had severe CTE; lawsuit is filed against the Patriots and the league.

BOSTON» Former New England Patriots star Aaron Hernandez had a severe case of the degenerative brain disease chronic traumatic encephalopathy, researchers said Thursday. His lawyer announced a lawsuit against the NFL and the team for hiding the true dangers of the sport.

Dr. Ann McKee, the director of the CTE Center at Boston University, said Hernandez had Stage 3 (out of 4) of the disease, which can cause violent mood swings, depression and other cognitive disorders.

“We’re told it was the most severe case they had ever seen for someone of Aaron’s age,” attorney Jose Baez said.

Hernandez killed himself in April in the prison cell where he was serving a life-without-parole sentence for murder. Baez said Hernandez had shown signs of memory loss, impulsivity and aggression that could be attributed to CTE.

“When hindsight is 20/20, you look back and there are things you might have noticed,” he said. “But you don’t know.”

CTE, which can only be diagnosed in an autopsy, has been found in former members of the military, football players and boxers and others who have been subjected to repeated head trauma. A recent study found signs of the disease in 110 of 111 NFL players whose brains were inspected.

The lawsuit filed in U.S. District Court claimed that the league and Patriots failed to protect their players’ safety, leading to the disease that deprived Hernandez’s 4year-old daughter, Avielle, of her father’s companionship.

“Defendants were fully aware of the dangers of exposing NFL players, such as Aaron, to repeated traumatic head impacts,” the lawsuit said. “Yet, defendants concealed and misrepresented the risks of repeated traumatic head impacts.”

NFL spokesman Brian McCarthy said the league had not yet seen the lawsuit and could not comment. A Patriots spokesman did not immediately respond to a message seeking comment.

The league recently agreed to pay $1 billion to retired players who claimed it misled them about the dangers of playing football.

The “loss of consortium” lawsuit filed on Thursday is independent of the classaction suit that began making payments this summer. Baez said it was the first of its kind.

“If we have to be groundbreakers in this area, it’s something we’re prepared to do,” he said.

Hernandez committed suicide a week after he was acquitted in the 2012 drive-by shootings of two men in Boston.

Prosecutors had argued that Hernandez gunned down the two men after one accidentally spilled a drink on him in a nightclub, and then got a tattoo of a handgun and the words “God Forgives” to commemorate the crime.

Hernandez did not raise CTE in his defense at either trial because he claimed actual innocence.