Paul Nicholls admitted his "sadness" after Kauto Star's time at his Ditcheat yard came to an abrupt end on Tuesday.
The winner of five King Georges and two Cheltenham Gold Cups had been officially retired in late October and was expected to remain at Manor Farm Stables in Somerset until Boxing Day, when he was due to parade at Kempton.
Owner Clive Smith had announced on Monday that the 12-year-old would be moving away to be prepared by European bronze medalist eventing rider Laura Collett and long-time Great Britain manager and coach Yogi Breisner for a new career in the world of dressage - a decision not popular with Nicholls and his staff.
The winner of 19 races for the champion trainer, including four Betfair Chases and two Tingle Creeks, Kauto Star had been with Nicholls for eight years and was invariably ridden by his head lad Clifford Baker.
Nicholls told his Betfair column: "It is with great sadness that I have to report that Kauto Star has left the yard for the last time. It has been no secret that Kauto's future has been a great source of debate since we announced his retirement. And, to be brutally honest, this morning I felt the time had finally come for me to take control of the situation, and to start making the decisions.
"Now, I am fully aware that Kauto is Clive's horse and he can do as he wishes, even though I would personally have loved Clifford to have looked after him for the rest of his years. But what upset me and my team here is when Clive announced that he had spoken to experts about the horse's future - but failed to consult and listen properly to the team that had looked after him here for the past nine years. That really upset us."
Nicholls went on: "So we had a team meeting here this morning. And after listening to everybody involved - there were about six of us in the meeting - I rang up Clive, said I don't want to fall out, but we think it is in the best interests of everybody concerned to take Kauto to Yogi Breisner's this afternoon so that he could start his new career in the dressage field as soon as possible.
"Which we did with the saddest of hearts. But I like to think with a lot of dignity, too. And, yes, there were plenty of tears too. He was a member of the family here at Ditcheat, and we will all miss him so much. I would just to like say that it was a privilege for us here at Ditcheat to train the horse. Good luck, old boy. You were the best - and deserve the best."
Collett, 22, who is an aspiring Olympian based at the Membury Estate in Wiltshire, tweeted: "I feel very privileged and extremely honoured to have been asked to ride Kauto Star. I will be working closely with Yogi to give Kauto Star the best chance of a second career in dressage."
She later added: "Kauto Star has arrived safe and sound. Had a nice roll, now happily munching on his hay!"
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