Native River will not get the chance to win another Cheltenham Gold Cup after being sidelined by a suspensory injury.
Winner of the race in 2018, he would have been heading back to the Festival next month aiming to become the first horse since Kauto Star in 2009 to regain the blue riband.
The 10-year-old had appeared back to his best this season, winning at Aintree and recently claiming the Denman Chase at Newbury.
He was also prominent in betting for the Grand National, although his participation in that race had still to be confirmed.
“Unfortunately we've had to scratch Native River from the Gold Cup. He's picked up a suspensory tendon injury, which means his season is over,” trainer Colin Tizzard's son and assistant Joe said:
The Tizzards still have a valid Gold Cup contender in their yard, with Betfair Chase winner Lostintranslation.
Native River had been around the 10-1 mark with the market trimmed slightly because of his withdrawal.
Coral now make Santini their 100-30 favourite (from 9-2), with last year's winner Al Boum Photo a 7-2 chance and Delta Work 9-2.