Star all-weather sprinter Kachy suffered a fatal injury Feb. 15 at Lingfield.
Trained by Tom Dascombe and owned by David Lowe, the 7-year-old was being readied for a defense of his All-Weather Sprint crown at Lingfield on April 10.
Sent off as the favorite to make it six wins from seven all-weather starts, Kachy displayed his customary dash from the gates to assume the lead, but heading down the back straight jockey Richard Kingscote was forced to pull up the speedy son of Kyllachy.
Lowe tweeted: "RIP Big fella. You were our world and will be missed forever." Lowe had said Kachy's final start would be at the All-Weather Championships Finals Day before he was retired to stud.
Kachy was unbeaten in two starts as a juvenile, including the Fairmont Molecomb Stakes (G3), and added two listed contests. He also finished second in the 2017 Commonwealth Cup (G1) and was third behind Blue Point in last season's Diamond Jubilee Stakes (G1) at Royal Ascot.
The horse won nine of his 28 starts, including five on the all-weather, for earnings of just over £470,000 (US$643,623) in a five-year career.
Harry's Bar won the six-furlong handicap Saturday, and the winner's trainer, James Fanshawe, added his own condolences, tweeting: "Thoughts go out to the Tom Dascombe stable. Kachy has been a real star. On his day, one of the best sprinters in the country."