Tributes to Silver Streak have flooded in after the top hurdler suffered a fatal injury.
Trainer Evan Williams said it was a "sad day" following the loss of the "one in a million" Grade 1 winner.
Grey in colour, akin to his name, the eight-year-old was one of the most popular National Hunt horses in training.
He had been due to defend his Christmas Hurdle crown at Kempton's King George meeting.
Williams tweeted on Friday evening: "Sad day Silver Streak suffered a fatal injury today thanks for the memories."
In last year's top level contest, held on Boxing Day, the talented hurdler comprehensively reversed form with Epatante from the 2019 renewal.
Silver Streak came home six-and-a-half lengths clear from the 1-5 favourite, eased in the closing stages by Aidan Coleman.
The Welsh raider, owned by Les Fell, finished sixth behind the mare in the 2020 Unibet Champion Hurdle.
He contested the past three renewals, belying his odds of 80-1 to take third in 2019.
Three of his eight wins, including his biggest success over the festive period, were recorded at Kempton.
The 2018 Welsh Champion Hurdle and Swinton Handicap Hurdle were also on his record.
His achievements over jumps were particularly remarkable as he lined up in sprint Flat races at the start of his career.
Williams told the Racing Post : "He was one in a million for us and I can't speak highly enough about him – he's irreplaceable.
"His Christmas Hurdle victory will live long in all our memories. It can be a cruel old job sometimes but we're all aware of the risks."
Jockey Adam Wedge, who won on him four times, wrote on social media: "Thank you for some fantastic memories that I will never forget."
Fans also left many tributes to the son of Dark Angel, who won over £450,000 in prize money.
From 36 racecourse appearances, he was also placed on 14 occasions.
Saturday's Betfair Exchange Hurdle at Ascot had been a possible target for him, before he was confirmed for Kempton.
"Terrible news. A really lovely horse. So sorry for all connections," one person wrote.
A second person said: "Ah Evan and team, that's awful. He was such a genuine horse and always very competitive. Glad he gave you some great days on the racecourse and got his G1 (Grade 1) too."
While a third added: "How incredibly sad for you all. He was a superb horse, a real favourite of mine and many others, always tried his best and entertained with his attacking style. Condolences to all your team, his owners & @Adamkwedge."
