Grand National-winning jockey Liam Treadwell has died at the age of 34.
Treadwell sprang one of the biggest surprises in the world's greatest steeplechase when riding 100-1 outsider Mon Mome to victory in 2009 for trainer Venetia Williams, on his first attempt.
He was also third on Monbeg Dude in 2015.
Other big-race successes for Treadwell included the Grand Sefton Handicap Chase at Aintree on Bennys Mist in 2015 and the Byrne Group Plate on Carrickboy at the Cheltenham Festival in 2013.
Treadwell announced his retirement from riding in February 2018, but returned to the saddle in March 2019.
As well as still riding, he was assistant to trainer Alastair Ralph, who described Treadwell's death as "unbelievably sad" and a "big shock".
Treadwell rode more than 300 winners during his career.
Williams said of his untimely passing: "It's a massive shock. I think we all thought he was in a good place now, having been through some tough times in previous years.
"We thought his renewed career had put in him in a situation where he was happy. It's desperately sad news."
But it was that day at Aintree 11 years ago that stands out for Mon Mome's trainer, who added: "We shared a day that was certainly the best day of my life, and I suspect of his.
"Liam rode many winners for us, but over and above that he was such a lovely person and, ironically, always such a happy person.
"I remember Dandy Nicholls ringing me up many years ago to tell me about this young lad who thinks he can do the weight on the Flat, but he can't, and he wants to come to you to ride over jumps.
"He was here for a large part of his racing career, and not a day went by without him putting a smile on somebody's face."
Mick Fitzgerald - also a Grand National-winning rider having landed the Aintree spectacular aboard Rough Quest in 1996 - is a former weighing room colleague of Treadwell's.
He told Sky Sports Racing: "Seeing him winning the Grand National is in many ways the best way to remember him.
"He was a really nice guy, he was a lovely rider - and it's just awfully sad. It's sad for his family and anybody connected with him. It just highlights again how precious life is.
"We used to call him 'Tredders'. He just got on with it when he was racing. You never knew he was there. He wasn't a shouter. He just wanted to do the best he could, and it's just awfully sad for everybody involved."
The British Horseracing Authority's chief executive Nick Rust also paid tribute, saying in a statement: "We are devastated to hear the tragic news about Liam Treadwell.
"Liam had a fine career in British racing, riding over 300 winners in the 17 years that he held a jockeys' licence, obviously none more memorable than his remarkable 100-1 Grand National success on Mon Mome in 2009, a ride that cemented his place in racing folklore.
"The racing community will be united in grief today, and the thoughts of everyone at the BHA are with Liam's friends, family and colleagues."
It is so sad to hear the news of Liam Treadwell's pasing he was a brilliant Jockey and one of the nicest kindest people you could ever meet all of our thoughts are with his Family RIP Treaders— Barry Geraghty (@BarryJGeraghty) June 23, 2020