The British Horse Racing Authority is to investigate after a 50-1 outsider won a race at Yarmouth by mistake.
The sport was left acutely embarrassed when it was discovered that the Charlie McBride-trained Mandarin Princess, winner of the opening two-year-old race at the Norfolk course, was in fact stablemate Millie's Kiss.
The error was only discovered after the outsider had overturned 4-6 favourite Fyre Cay in the six-furlong novice auction stakes for juveniles. But as the weigh-in had been announced, the result was allowed to stand - for the time being.
Millie's Kiss, a three-year-old with plenty of racecourse experience, was due to run in the nine-furlong handicap later on the card but was subsequently withdrawn.
A report issued by the Yarmouth stewards read: "The stewards held an inquiry to consider the circumstances surrounding the identification of the winner, Mandarin Princess, trained by Philip (Charlie) McBride, which was presented at the sampling unit for routine testing. The scan identified the horse to be Millie's Kiss, the trainer's other runner in race four.
The BHA said in a statement: "The responsibility lies with the trainer to present and run the correct horse in the race. Having said that, and while we have not seen an incident of this nature in recent times, we will of course determine what steps need to be put in place to prevent it from happening again.
"We sympathise with the betting operators and betting public who have potentially been affected by this incident."
John Egan, who rode the 'winner', believes the stewards should have declared the race void. He told At The Races: "At the end of the day, we're all human. Mistakes happen. I feel most sorry for Charlie. I'm surprised on the day the stewards didn't make the race void or disqualify the winner."