King Charles III's first runner had to settle for second behind a horse ridden by the Queen's Gold Cup jockey.
Educator was the 11-10 favourite with the bookmakers to make a winning start for his owner at Salisbury. But he was comfortably overturned by Okeechobee (7-4), the second choice of punters in the four-runner field.
Ryan Moore, who gave the Queen one of her best racing moments when Estimate took the 2013 Gold Cup at Royal Ascot, was in the saddle.
The jockey guided Okeechobee to the front with around two furlongs to race in the Radcliffe & Co Handicap and kept up the gallop by four-and-a-quarter lengths.
Tom Marquand, wearing Her Majesty's royal purple, red and gold silks inherited by the King, asked the William Haggas-trained Educator for his effort. However, on his first start since winning a Newmarket handicap in April, the one-time Derby hope had no more to give on the good to soft ground.
Okeechobee earned connections £11,500 on the back of his impressive performance.
Moore reported to Harry Charlton, who trains the winner with his father Roger, that he thought he would not triumph aboard the half-brother to St Leger hero Logician.
"He said 'I couldn't tuck in, I have to roll forward, I can't go behind them.' So he was in an awkward position," Charlton said.
"I think he (the horse) caught him by surprise. Ryan was very impressed with him when he rode him at Kempton, how good natured he was and how push button he was.
"He jumped forward from stall 14 and then took him back. He expected him to do the same today.
"Ryan was impressed he could still pick up. He said the others kind of faltered three (furlongs) down and he didn't want to go on that early, but had to. It was another test for him and he has come through it."
Educator was the first horse to race in the royal colours since Improvise on September 8, the same day the Queen died at her Balmoral estate in Scotland.
British Horseracing Authority chairman Joe Saumarez Smith said in a statement ahead of the race: “The loss of Her late Majesty was keenly felt within the racing and breeding industries given her lifelong passion for the sport, and so we are naturally thrilled to see that the horses previously owned by her will race on in the ownership of His Majesty King Charles III.
“Her late Majesty Queen Elizabeth II left an indelible mark on our sport and her legacy will continue to be felt, not only through the horses that will continue to run in the name of King Charles III but also those she bred who are yet to be seen on the racecourse in the years to come."
