Ruby Walsh has stepped down as number one jockey to former champion trainer Paul Nicholls.
Grand National-winning rider Daryl Jacob has been promoted to the top position at Nicholls' Ditcheat yard.
Nicholls and the 34-year-old Walsh had struck up one of the most successful partnerships in jumps history, with the great Kauto Star central to the success story.
The Irish-based jockey, who had been attached with Nicholls for nearly 11 years, cited travel demands as being one of the chief reasons for the split.
Nicholls told his Betfair column: "Daryl takes over as the number one, and I am as delighted for him as I am sad to see Ruby go - Daryl has earned his chance.
"Myself and Ruby have been chatting for the past couple of months. It was clear that the constant travelling to and from Ireland, with his wife Gillian and the girls at home, was becoming a bit of a grind for him.
"It would have been exhausting for someone young and single, let alone a grey and ageing family man.
"But he was getting up before 5am, and not getting home until after 8pm, when riding over here - before his girls got up in the morning, and after they went to bed most nights - and when you have a young family that must really take its toll.
"So, for personal rather than professional reasons, he has taken the decision to end his near 11-year role as stable jockey at Ditcheat, having started here in October 2002, to concentrate on riding in Ireland.
"He came over to explain his decision on Saturday, and we both agreed it was the best way forward in the circumstances.
"After he had left for the airport, I texted him to say, 'Thanks for all the magic moments'.
"And he texted back, 'Magic, they were. And you made the success I have had, which made today the hardest call I have ever made. Thanks for the way you reacted, a gentleman and a friend'.
"That really meant a lot to me. He and his family have been coming to Ditcheat for as long as I can remember, and the bond our families have formed down the years will remain, whatever happens."
Walsh, who will remain top jockey with Irish champion trainer Willie Mullins, will still ride for Nicholls in the future.
Nicholls said: "It isn't as if he is severing all his ties here at Ditcheat anyway, as he will continue to ride for us this season and in the future when he is needed and when he is available.
"You don't let someone of Ruby's calibre - he must have ridden 600-odd winners for us and been instrumental in nurturing the careers of Kauto Star, Denman, Master Minded and Neptune Collonges, as well as our current stars Big Buck's, Silviniaco Conti, Zarkandar and Al Ferof - go un-used.
"Ruby had a difficult and unenviable job trying to satisfy both myself and Willie (Mullins) down the years, so at least that's another weight off his mind, as well as the travelling.
"Above all, though, we respect each other and are more friends than anything else."
"Being stable jockey there enabled me to ride in, and win, the biggest races in our sport, so walking away from my position as stable jockey was never going to be easy" - Ruby Walsh on his role with Paul Nicholls
Walsh said Nicholls has been "responsible for some of the most amazing days of my life".
He told the Irish Examiner: "I started as Paul's stable jockey in October 2002, but when I chose to live in Ireland, this was always going to be a job that involved a lot of travelling.
"Paul has never been anything but fair and honest since our association began and has been responsible for some of the most amazing days of my life.
"From King Georges and Tingle Creeks, to Champion Chases, World Hurdles and Gold Cups, he has been behind them all.
"With horses like Kauto Star, Denman, Master Minded, Azertyuiop, Strong Flow and Twist Magic, to the current stars Big Buck's, Silviniaco Conti and Al Ferof, great horses were, and still are, a staple diet in Ditcheat.
"Being stable jockey there enabled me to ride in, and win, the biggest races in our sport, so walking away from my position as stable jockey was never going to be easy.
"However, I felt towards the end of last season that the travelling was starting to take its toll - my family and I were like passing ships in the night."
Walsh's first keynote success for Nicholls was aboard Cenkos in the 2002 Tingle Creek at Sandown, which was followed up later in that campaign by Azertyuiop's Arkle triumph at the Cheltenham Festival.
Azertyuiop went on to win the Queen Mother Champion Chase a season later.
Other big Nicholls-Walsh winners in that season included Cornish Rebel in the Challow Hurdle at Newbury and Strong Flow in the Feltham Chase at Kempton.
Another Challow success came in 2006 when Denman won by an unchallenged 21 lengths.
The pair would later team up for victories in the Royal & SunAlliance Chase and the Lexus Chase before Denman claimed an extraordinary success in the 2009 Hennessy at Newbury.
Master Minded was also a deeply significant horse in the Nicholls-Walsh axis.
The Clive Smith-owned gelding won eight races for Walsh, including back-to-back renewals of the Champion Chase in 2008 and 2008.
Perhaps of even more importance was Big Buck's, the magnificent staying hurdler who landed four consecutive World Hurdles for Walsh at the Cheltenham Festival.
Kauto Star is, however, indisputably the greatest thoroughbred Walsh has ridden for Nicholls.
The legendary chaser was described by the jockey as "a horse of a lifetime" after he partnered the now-retired 13-year-old to 17 victories, including two Gold Cups at the Cheltenham Festival and five victories in the King George at Kempton.
Other Nicholls-trained, Walsh-ridden Grade One winners included Celestial Halo, Fiveforthree, Taranis, Twist Magic and Neptune Collonges.
Walsh, whose last big-race triumph for Nicholls was aboard Zarkandar in the John Smith's Aintree Hurdle in April, said the decision to walk away required much thought.
He said: "In my eyes there was never going to be an easy or right time to make the decision to leave Paul's yard, and all it entails, behind me.
"Ditcheat is a much bigger place now than when I started there. While Kauto and Denman are gone, the rebuilding process is well advanced and Silviniaco Conti, Al Ferof, Big Buck's and Zarkandar are hard horses to give away the ride on.
"However, at 34 years of age, I no longer feel I can give 100% to two yards - and being a bit-part player will only hinder both."
Walsh said the decision to part company from Nicholls was also made in a bid to extend his career.
He said: "The future for me will be Naas instead of Newbury, and Navan instead of Haydock, but it will also be home for dinner with Gillian (Walsh's wife) and the girls rather than a quick coffee and breakfast.
"I also hope this decision will enable me to prolong the career I love for years to come.
"My future will be very different, and probably a bit strange, but I think it is still bright as Willie Mullins' yard is well stocked with talent and hopefully some future stars.
"What I have left behind is a powerful yard, headed up by a gentleman, and friendships made for life."