The Mick Price and Michael Kent Jnr-trained I'm Thunderstruck was euthanised on Thursday afternoon following arthroscopic fetlock surgery.
In a post on social media, Price Kent Racing said I'm Thunderstruck had suffered a catastrophic knee injury whilst getting up after a general anaesthetic.
"On behalf of all our owners and staff we are heartbroken," the post read.
Syndicator OTI Racing said in a post: "Words cannot adequately express our sadness at today's new on I'm Thunderstruck. We feel for all connected with this amazing horse – our co-owners and the team at Mick Price Racing in particular. We will remember him in full flight."
Price and Kent had decided to end I'm Thunderstruck's autumn campaign after a track gallop at Cranbourne on Tuesday after hoping to get the gelding to Sydney next week for the Group 1 Queen Elizabeth Stakes (2000m) at Randwick.
At his last start, I'm Thunderstruck ran the worst race of his career finishing 11th behind Mr Brightside in the All-Star Mile (1600m) at Moonee Valley on March 18.
I'm Thunderstruck raced on 23 occasions, collecting seven wins, including the Group 1 Toorak Handicap, the Group 1 Makybe Diva Stakes and The Golden Eagle, along with eight minor placings and more than $8.3 million in prize money.