Sam Twiston-Davies is to go freelance and will be replaced by Harry Cobden as number one jockey for 10-time champion jumps trainer Paul Nicholls.
Twiston-Davies had been in the role for four years, although Nicholls expects he will still ride regularly for him.
“It’s my decision to go freelance and now that I’ve made it I am going to give it everything I’ve got,” the 25-year-old told the Racing Post.
Nicholls said there had been no falling out between the pair.
“We’re still all mates, it’s just a restructuring on both sides,” he said.
Twiston-Davies rode 145 winners in his first season as stable jockey for Nicholls, including the Queen Mother Champion Chase on Dodging Bullets.
His total of 108 winners in 2017-18 – when he had six weeks out through injury – was his lowest since, with Cobden, Bryony Frost and Sean Bowen among other jockeys used by Nicholls.
Despite the new arrangement, Nicholls said: “I expect Sam to have as many rides and winners for me over the next 12 months as he did during the last season.”