Henrietta Knight has announced her retirement, the three-times Gold Cup-winning trainer said on her website.
Knight, 65, will give up her National Hunt licence to spend more time with her husband, Terry Biddlecombe, who suffered a stroke last October.
The Oxfordshire trainer will forever be remembered for her expert handling of Best Mate, who won three consecutive Gold Cups at the Cheltenham Festival between 2002-04.
Knight said on www.henandterry.com: ''After much deliberation, and largely due to my husband Terry Biddlecombe's continued ill health, I have decided to hand in my trainer's licence.
''I have been incredibly lucky to have experienced some wonderful moments since I first began training in 1989.''
Based in Wantage, Oxfordshire, Knight has saddled over 700 winners.
She is due to relinquish her licence next month.
Knight said: ''I am hugely grateful for the backing that I have received over the past years from my family, my loyal owners, my dedicated staff and from numerous top jockeys.
''Likewise the press and media have always been tremendously supportive.
''I would like to thank everybody who has helped me enjoy so many happy days.
''However, despite the above mentioned decision, I still intend to retain links with the racing world.
''My neighbour and close friend, Mick Channon, has agreed to continue to train the majority of the horses which are currently in my care.
''He, too, enjoys the National Hunt scene and is already making his presence felt in that sphere with recent good winners from only a handful of National Hunt runners.''
Knight began training in July 1989 and secured her first winner, The Grey Gunner, at Bangor a month later.
Despite her defining association with Best Mate, Knight was also responsible for Edredon Bleu, who won the Queen Mother Champion Chase at Cheltenham in 2000 and the King George VI Chase at Kempton in 2003.
The tough chaser also claimed four renewals of the Peterborough Chase at Huntingdon between 1998-2001 during a brilliant career.
Other significant horses in Knight's care include Impek, Racing Demon and, most recently, Somersby, who provided the trainer with her last Grade One winner in the Victor Chandler Chase in January.
She said: ''I hope that this change will mark the beginning of a new era and I am looking forward to continuing to handle the horses until they move to West Ilsley for their races.
''My gallop, schooling fences and loose jumping school will have plenty of use and other new projects are already in the pipeline.
''There are exciting days ahead.''
Best Mate's breathless rise took Knight to a new level and put her upon a pedestal with the racing public.
In addition to his three Gold Cup wins, the Jim Lewis-owned chaser was also victorious in seven other Graded races, including the King George VI Chase at Kempton in 2002.
He died on the racecourse in November 2005 when suffering a heart attack during the Haldon Gold Cup at Exeter.
Knight said the time was right to announce her retirement.
She said: ''Terry hasn't been terribly well and he had a stroke last autumn and doesn't get around quite as much as he used to.
''It's difficult for me to do trips to racing and go away from home.
''Now I'm 65 it's probably time to hand over to younger people.
''We've had some marvellous times in racing and I've thoroughly enjoyed every moment of it.
''We've had some wonderful days.''