Kyle Busch died from severe pneumonia that progressed into sepsis, the Busch family confirmed Saturday. Dakota Hunter, vice president of Kyle Busch Companies, relayed the medical evaluation, which stated the infection overwhelmed Busch's body with rapid and fatal complications. Busch, a two-time NASCAR champion, passed away at 41 on Thursday.

The timeline shows how quickly the illness took hold. Busch became unresponsive during a simulator session in Concord, North Carolina, on Wednesday and was rushed to a Charlotte hospital. A 911 call obtained by ABC reveals he reported shortness of breath, feeling overheated, and coughing up blood. He had also told his team he needed a doctor's shot after racing at Watkins Glen on May 10 with a sinus cold.

Busch won 234 races across NASCAR's top three series, more than any driver in history. All 39 drivers will race with a black No. 8 decal on their car Sunday to honor him.