Mystery surrounds the termination of Johnny Murtagh's contract as retained rider for Aga Khan's Irish-trained horses.
The 42-year-old was offered the role in November 2010 after resigning as stable jockey for Coolmore and few details were released as to the reason for his departure.
A statement issued on Thursday by Murtagh read: "I was informed yesterday afternoon that my contract to ride for His Highness the Aga Khan was being terminated with immediate effect.
"I would like to take this opportunity to thank His Highness and his staff at his studs in Ireland and France for the very successful years we have had together, and to sincerely wish them every success in the future."
The Aga Khan, one of the most notable owner-breeders in the sport, has enjoyed a great deal of success with Murtagh, particularly during the rider's first spell as stable jockey to trainer John Oxx.
He guided Sinndar to victory in the Epsom Derby, the Irish Derby and the Prix de l'Arc de Triomphe in 2000, part of 18 Group One wins he won for the Aga Khan during the period, and took the French Oaks in his green and red silks aboard Valyra this June.
Aga Khan's Irish stud farm manager, Pat Downes, said there had been "differences between the parties".
He said: "I can confirm it (Murtagh's departure) is true.
"I don't have a whole lot more to say, other than there were differences between the parties and it was agreed that we would part."
Murtagh is currently injured after sustaining a hairline fracture to a small bone under an eye when kicked by his mount, Lottie Dod, in the preliminaries before the Phoenix Stakes at the Curragh on August 12.
He does, however, have a link with another increasingly influential owner in Irish racing in Andrew Tinkler, who fairly recently moved the majority of his string to Tommy Carmody.
Carmody rents stables at the Curragh owned by Murtagh and he has ridden winners for the operation.
Last weekend, Carmody's Ursa Major also inflicted a notable defeat upon the Aga Khan's Hartani in the Gain Horse Feeds Irish St Leger Trial Stakes.
Tinkler's racing manager, Tim Jones, said it was "inappropriate" to make any comment.
The Aga Khan announced on Monday Christophe Lemaire had penned a contract to remain as his jockey in France until the end of 2013.
In the last couple of weeks, Lemaire has won the Secretariat Stakes and the Yorkshire Oaks in his silks.
At the time of Murtagh's appointment, the Aga Khan said: "We have had some wonderful days in the past and we look forward to renewing our successful association.
"I believe it is vital to the continued success of my bloodstock operation to have a retained jockey in the countries where my horses are trained.
"This has been the situation in France for many years and I am most pleased now to have a similar arrangement in Ireland."
Murtagh has ridden 46 winners so far this year in Ireland and five of his top six money-earners have been Oxx-trained Aga Khan horses, such as Takar and Sharestan, while he has won minor races on horses for the owner's other Irish trainer, Michael Halford.
Murtagh has been on hand to land some of the big British prizes, teaming up with Oxx's Saddler's Rock, who is owned by Michael O'Flynn, in the Goodwood Cup and taking the King Edward VII Stakes at Royal Ascot on the Sir Henry Cecil-trained Thomas Chippendale.
Oxx was unavailable for comment.