The horse collapsed moments after beating Thistlecrack in the Cotswold Chase at Cheltenham’s Festival Trials Day.
His trainer Oliver Sherwood described him as “the horse of a lifetime”.
He said: “He’s been the horse of a lifetime and I always said he would die for you and he’s died for me and the team today doing what he does best.
“He wanted to win that race, he was beaten and then fought back in the last 50 yards to win.
“It’s sad for Trevor and my team at Rhonehurst, I’ve been in the game 32 years and horses like that don’t come along very often.”
Nathan Horrocks, who rides Many Clouds on the gallops, told Racing UK: “It’s a shock, from shouting him home to 10 minutes later he’s not even with us. He’s a massive loss for everybody, he’s of huge importance to the yard but also to Lambourn and the sport.
“He captured the nation, but that is our sport - it makes us love it and hate it. What was great about him, and was also his downfall, was that he didn’t know when to quit.”
The 2015 Grand National winner collapsed metres after crossing the finish line earlier this afternoon. Screens were erected around the popular bay gelding, but racegoers were later told that he had died.
Colin Tizzard, trainer of Thistlecrack, said: “This is sad as can be. A fantastic and lovely horse.”
Many Clouds first shot to prominence when winning the Hennessy Gold Cup Chase in 2014, before surpassing that result with a brilliant victory in the Grand National the following April.
Lancashire Post readers also took to social media to share their memories of Many Clouds.
Alan Hudson said: “Great horse, backed it when it won the National.”
Katie Eames said: “He was a gorgeous boy and a wonderful racehorse but sadly no more.”
It is believed the horse died of a heart attack.