Laminitis. I read she dropped a foal (colt) in the a.m. and was euthanized in the p.m. One day before turning 18. Time flies.
https://www.thoroughbreddailynews.com/legendary-australian-sprinter-black-caviar-dies-following-laminitis-disease/
Royal Ascot
https://www.youtube.com/watch?v=sP0t14-SHWE