Champion jockey Tony McCoy is leaving the Martin Pipe yard to be the contracted jockey to J. P. McManus.
The move will mean McCoy becomes, in effect, stable jockey to Jonjo O'Neill and will become the best-paid jump jockey ever.
The split with Pipe is believed to be amicable, although the trainer is understood to be disappointed by McCoy's decision.
McCoy has been champion jockey for nine consecutive years and freely admits that it would have been impossible without his partnership with Pipe, who has won the trainers' title a record 14 times.
McCoy told the Daily Telegraph: "It's going to be a huge change in my life. I'm very much looking forward to it. I hope to continue to do a good job and will still be trying very much to be champion jockey.
McCoy, who has ridden more winners than any other jump jockey in the sport's history, suffered a broken arm last June and a fractured cheekbone in February but still beat off the challenge of Richard Johnson to take the 2003/04 championship with 209 winners. Of those, 116 were for Pipe.
McCoy (29), also reached a career milestone in January when Magical Bailiwick's victory at Wincanton took him to the 2,000 mark in Britain - a remarkable feat considering the first of those winners came just less that 10 years ago.
"Today was also one of the saddest days of my career," added McCoy. "Martin and his family have been my family for the past eight years. I owe him everything that I've achieved in the last eight years.
"I'll always be indebted to him, the staff, the owners and the horses at Pond House. I hope to continue to ride for him whenever possible. He's a genius."