Jamie Spencer has resigned from his position as stable jockey to leading Irish trainer Aidan O'Brien.
Speculation had been rife over the last 24 hours that the rider had left one of the highest-profile jobs in racing.
Coolmore spokesman Richard Henry confirmed the news in a statement this evening:
"Jamie is a young jockey with a lot of talent and has a long career ahead of him. All the team at Ballydoyle wish him the very best."
Spencer was under pressure last year in his first season in his high-profile role with O'Brien, and he was stung by criticism of some of his rides.
But he ended the year as Ireland's champion at the age of 24 and his link-up with the Ballydoyle stable produced late-season Group One winners in Ad Valorem (Middle Park Stakes) and Oratorio (Prix Jean-Luc Lagardere).
However, there were plenty of low points, too, in a poor year for the powerful operation, in particular defeats for the likes of One Cool Cat, Antonius Pius and Powerscourt.
Spencer was disqualified on Powerscourt after finishing first in the Arlington Million, and was then criticised by some for committing too early on him in the Breeders' Cup Turf.
He also came under fire in some quarters for his ride on the frustrating Antonius Pius, who finished second in the Breeders' Cup Mile.
Johnny Murtagh is now hot favourite to be crowned Irish champion Flat jockey this season.