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"Uneasy lies the head that wears the crown,"  Shakespeare wrote in "Henry IV, Part Two." It was certainly true of a later portly potentate.

Mad, sad, plagued by memory problems and and prone to unpredictable rages late in life, Henry VIII may have suffered repeated traumatic brain injuries similar to those experienced by some NFL players, according to a new study from the Yale Memory Clinic.

[The ghost of Ken Stabler haunts Super Bowl L]

The Tudor king suffered two major head injuries during jousting tournaments. In 1524 a lance struck him above the eye through his helmet's open visor, dazing him. Although he continued to joust, he suffered migraines afterwards. Then, on Jan. 24, 1536, the 44-year-old monarch's fully armored horse fell on him, knocking him out for two hours. In between, while out hawking, Henry fell on his head and briefly lost consciousness when the stave he was using to vault across a brook broke in half.

“It is intriguing to think that modern European history may have changed forever because of a blow to the head,” said neurologist Arash Salardini, lead author of the study, in a press release.

About the 1536 incident, a court chronicler wrote that "... [Anne Boleyn] tooke a fright, for the King ranne that tyme at the ring and had a fall from his horse ..."

Within months of the nearly fatal accident, Boleyn, the second of Henry's six wives, was beheaded so that he could marry Jane Seymour. (Fifth wife, Katherine Howard, was also executed.) From that point, until his death in 1547 at age 55, the formerly even-tempered, thoughtful military strategist became increasingly moody, forgetful and impulsive, according to the paper published online this week in the Journal of Clinical Neuroscience.

"A contradictory picture of Henry's character emerges from history," the authors write in the study. "[He] was a vigorous, generous and an intelligent king; who saw early military and naval successes. In contrast, in his later years he became cruel, petty and tyrannical. His political paranoia and military mis-judgments are in direct contrast to his earlier successes and promise."

Personality changes, memory loss, angry outbursts and progressive dementia are hallmarks of chronic traumatic encephalopathy, a progressive degenerative brain disease resulting from repeated blows to the head. More than 100 football players have been diagnosed, postmortem, with CTE. In the past two weeks, two former Super Bowl champions were added to the list: Oakland Raiders quarterback Ken Stabler, who died recently at age 69, and 27-year-old Giants safety Tyler Sash, dead from an accidental overdose of painkillers in September.

[Concussion syndrome plagued former NFL player Tyler Sash]

Henry VIII suffered numerous health problems during his life — only about 10 percent of the population at the time survived past age 40 — and scientists through the ages have hypothesized the possible causes, including syphilis, diabetes and Cushing syndrome.

The Yale researchers, however, believe that CTE best explains Henry's behavioral abnormalities. Two potential side effects of traumatic brain injury are growth hormone deficiency and hypogonadism. The former can impair concentration and memory, the latter can lead to impotence. Historians believe that while the king was very much a womanizer in his youth, he had difficulty completing sexual intercourse from the time of his marriage to Anne Boleyn.

Perhaps it wasn't all Henry's fault. None of his wives were particularly well suited for him, according to a 2014 study by British historian Elizabeth Norton. In performing a psychological study of the king and each of his six wives and then using the online dating site eHarmony to rank compatibility, only Anne Boleyn came close to a match, mostly because she shared "high energy" and "ambition" with her husband.

But we all know where that got her.