The Queen was among the first to learn that reigning champion Flat trainer Richard Hannon is to hand over the licence to his son Richard junior on January 1.
Roles will be reversed as the Wiltshire-based handler, 68, who has been at the helm for 43 years, will assist his son, who celebrated his 38th birthday yesterday.
"It was always going to happen, but Richard junior has served his apprenticeship and you cannot keep him waiting forever," said the trainer.
"We thought long and hard as to when to make the announcement, but I wanted to make sure all my owners knew first, especially the Queen, and now that all the yearlings are in for next season it is the appropriate moment to let everyone know," he explained.
"Inevitably, people will say that I have retired, but I will still be up and out at first lot and assisting Richard instead of him assisting me."
Hannon, crowned champion trainer three times in the last four years, secured numerous big-race victories, including three triumphs in the 2000 Guineas with Mon Fils, Don't Forget Me and Tirol.
He lifted the 1000 Guineas this year with Sky Lantern, ridden by Kildare-born Richard Hughes, his stable jockey and son-in-law.
Hannon began training in 1970 following the retirement of his father, Harry, and bows out at the top after securing a record-breaking number of domestic winners (238) to earn over £4.5million in prize-money.
Meanwhile, Roi Du Mee claimed some major scalps when stealing a shock Grade One victory at the Down Royal Festival earlier this month, in the feature JNwine.com Champion Chase.
But Gordon Elliott's improved eight-year-old faces an even more daunting task at Haydock tomorrow in a vintage Betfair Chase field that includes the Ulster-bred Gold Cup hero Bobs Worth.
Despite cruising to a 13-length rout over Sizing Europe and First Lieutenant at Down Royal, the 13-time winner is as big as 20/1 to secure a first Irish-trained win.