High-class filly Somehow has been put down after fracturing a cannon bone.
Aidan O'Brien's four-year-old won five of her 12 starts including the Group Two Dahlia Stakes at Newmarket in May.
She was last seen filling the runner-up spot in the Tattersalls Gold Cup at the Curragh.
O'Brien said: "Unfortunately Somehow has suffered a fatal injury. She got a fracture behind on her cannon bone and we were unable to fix it.
"It's a real pity as she was such a good filly, and had progressed well this season."