Walter Swinburn, one of the most renowned jockeys of his generation and rider of the brilliant Shergar, has died, aged 55.
Nicknamed the 'Choirboy', Swinburn partnered Shergar to glory in the 1981 Derby at the age of 19, one of three winners for him in the Epsom Classic alongside Shahrastani (1986) and Lammtarra (1995).
Many other big-race successes around the world adorned his CV before his retirement in 2000.
Swinburn took over the training licence from his father-in-law, Peter Harris, in November 2004, sending out over 260 winners from his Hertfordshire base before handing in his licence at the end of October 2011, citing financial reasons.
Harris said: "I've been in Scotland all day and got home this evening and all I know is that he has died.
"I don't know any more details at the moment."
The cause of death was not released on Monday night.
Shergar was trained by Sir Michael Stoute, who said: "On the big days he was nerveless and he lived for those occasions. We had many, many very happy successful days. It's just so sad."
Newmarket-based James Fanshawe was assistant to Stoute when Swinburn was the stable's number one rider, and described him as a "brilliant jockey".
"Walter and I were at Sir Michael Stoute's together and he was a brilliant jockey," said Fanshawe, now a successful trainer in his own right.
"Obviously he won the Derby in 1981 at the age of 19 and won the Derby two more times, but he had the most sympathetic pair of hands as a rider. He was a real horseman and was good on the most difficult of horses.
"We worked there together for seven years."
The top-class miler Zilzal was another major Swinburn winner, with their successes including the Sussex Stakes and Queen Elizabeth II Stakes.
Fanshawe said: "Not many people could have ridden Zilzal. He was a brilliant horse, but had a fiery nature. Walter was brilliant on those sort of horses.
"His big-race record would stand comparison to anyone."
Swinburn won the Prix de l'Arc de Triomphe on the filly All Along in 1983 for Patrick Biancone, while the Breeders' Cup Turf came his way with the Stoute-trained Pilsudksi in 1996.
He landed the 1000 Guineas with Musical Bliss (1989), Hatoof (1992) and the majestic Sayyedati in 1993, with his 2000 Guineas success coming through Doyoun (1988).
Shergar went on to claim the King George VI And Queen Elizabeth Stakes at Ascot in his Derby year and Swinburn twice tasted victory in the Irish Derby, courtesy of Shareef Dancer in 1983 and Shahrastani in 1986
In 1987 he again teamed up with Stoute on the biggest stage to claim the Oaks aboard Unite 1987.
After his riding days were over, Swinburn enjoyed a successful period as part of the Channel 4 Racing team, working with former National Hunt great John Francome among others.
Francome said: "I spoke to him a couple of months ago and he seemed in really good form. It's absolutely shocking he should die aged 55. No age at all.
"He was an absolutely gifted rider, you never saw any horse pulling with him or having their head in the air.
"He was a little bit of a troubled soul in some ways, he had weight problems which probably affected him a lot more than other people, but that said that seemed to be a long time ago and he seemed to all intents and purposes fine, but obviously he wasn't.
"He could ride a race, he had a really good feel for what was going on underneath him. What the horse was doing - he must have been a fantastic jockey to have riding for you.
"He'd give great feedback and come back in and tell you everything you needed to know. He probably knew everything he needed to know by the time he got down to the start.
"He was a very sensitive person, both on and off a horse."
Swinburn suffered a terrible fall at Sha Tin in February 1996 when his mount Liffey River crashed through the rails and was in intensive care for a week with severe head and chest injuries.
He returned to win on his first ride back on Talathath at Windsor just six months later.
Francome added: "It was a shocking fall, and he made an amazing comeback - but he was happiest on a horse.
"He was great company and gave great insight (during television coverage). Flat racing is a little bit sharper than jumping and he could see what was going on in a jockey's mind.
"He had a good smile, great sense of humour, fabulous parents - just a really nice family and I'm devastated for them."
Of Swinburn winning the Derby so young, Francome said: "It was extraordinary wasn't it, like winning the Champions League in your first season playing football. But it happened and he used to take things in his stride.
"He was just a good lad."
The racing world was quick to take to Twitter to pay tribute, with Sir Anthony McCoy writing: "Very sad to hear about the death of Walter Swinburn. Brilliantly stylish & a genius in the saddle. A jockey that God hath retained. RIP."
Weighing-room veteran Steve Drowne said: "Shocking and sobering news of Walter Swinburn the owner of talent that most jockeys can only dream of #ripwally."
Trainer Richard Hannon said: Terribly sad news to hear the passing of Walter Swinburn. One of the best we have seen. Thoughts and prayers are with his family."
Former rider Michael Hills said: "Devastated to hear about Walter Swinburn, great friend, wonderful times, Genius in the saddle. Thoughts are with his family. Gone too soon."