Smart Melody, rated among Australia's best three-year-old fillies, has died following complications after colic surgery.
Trained by Kris Lees, Smart Melody had only last week returned to pre-training after a spring campaign that stamped her as a horse of the future.
Lees confirmed the death of one of his stable stars on social media.
“It is with a heavy heart we announce the loss of Smart Melody today to a colic-related illness,” the stable posted on Twitter.
She advanced her unbeaten record to five with victory in the Group Two Thousand Guineas Prelude.
Smart Melody's winning run came to an end in the Group One Thousand Guineas and was sent to the spelling paddock to be readied for an autumn campaign.
The filly was in light work at Cojuangco's Gooree Park property ahead of a return to Lees' Newcastle stable.