Former Denver Broncos star Demaryius Thomas was found dead in his Atlanta apartment Thursday night, and his family said a seizure might be to blame. “He had been suffering from seizures for over a year, and we believe he had a seizure when he was showering,” LaTonya Bonseigneur, Thomas’ cousin, told the Associated Press. “We’re not sure when he died. We just spoke with him yesterday.” Bonseigneur said that on Thursday Thomas called his driver, who has a key due to previous seizures, and that’s who found Thomas.

Authorities confirmed they believed the cause of death was a medical issue, though they did not specify what it was. Thomas’ career was defined by his eight years with the Broncos, with whom he won a Super Bowl and multiple Pro Bowls. “We are devastated and completely heartbroken,” the Broncos said in a statement. “We were very much looking forward to celebrating Demaryius for years to come as one of the greatest players in franchise history.”