Former Detroit Lions running back Mel Farr died suddenly back in 2015 from a massive heart attack due to undiagnosed hypertension at the age of 70.

But now it turns out something else had gone undiagnosed—CTE. This is the traumatic brain injury synonymous with multiple concussions.

According to a report from ESPN’s Outside The Lines, Farr also had Stage 3 chronic traumatic encephalopathy, more commonly known as CTE at the time of his death.

We know this after Farr's family donated his brain and spinal cord to Boston University School of Medicine where, since 2008, researchers have been testing the brains of deceased athletes for the presence of CTE, the progressive degenerative brain disease associated with repeated blows to the head.

"Mr. Farr had Stage 3 CTE, which is consistent with other football players of similar age and exposure," Dr. Ann McKee, the director of Boston University's CTE Center told ESPN. "At Stage 3, the disease is widespread, but most severe in the frontal lobes as well as the medial temporal lobes, specifically the hippocampus, which plays a critical role in forming new memories, and the amygdala, which governs emotion.”

Farr, who was a 1967 first-round draft pick and NFL rookie of the year, played for the Lions from 1967 to 1973. He played college football at UCLA and high school football in his hometown of Beaumont, Texas. In total, he played the game for 18 years. His family's story will be part of an Outside The Lines special, "Football Forever" which will air this Saturday night on ESPN.

Definitely, worth a watch—especially if you have a child who plays football.

Outside The Lines talked to Farr's children about his behavior before his death.