Chicago Bears legend Dick Butkus died after suffering a stroke last month, according to the death certificate obtained by TMZ Sports.
We broke the story ... the Hall of Fame middle linebacker passed away on October 5 in his Malibu, CA home, and now we know what happened to the beloved football star.
The certificate, issued by Los Angeles Department of Health, shows "cerebrovascular accident" -- known more commonly as a stroke -- as the immediate cause of death.
There were secondary causes listed as well .