The wrong horse won a race at Yarmouth in England on Thursday at 50/1, defeating an odds-on favourite.
Mandarin Princess was declared the winner in the 2YO Novice Stakes over the 4/6 favourite Fyre Cay but was subsequently identified as the three-year-old stablemate Millie's Kiss which was supposed to run in a later race.
Both are trained at Newmarket by Charlie McBride who told the Racing Post he had made a mistake.
"It's a genuine mistake and humans make mistakes. It's an honest error and no-one stood to gain anything by it," McBride said.
"I took a young girl who has been with me for two or three months to the races. She's ridden both fillies and knows them both.
"After we checked them in we got some lunch and I sent her to get the two-year-old ready and I went to the weighing room to get the saddle.
"I like to weigh my horses out early but I had to wait over 20 minutes for the saddle. The filly was already out when I got back and as I was stressed and rushing I didn't look that closely - I just assumed it was the right horse."
The mistake was picked up at the post-race sampling unit and after correct weight had been declared.
An inquiry was called by the stewards, but no announcement regarding the result was made on course until nearly 45 minutes after the mistake had first been discovered and over two hours after the race had been run.
The racecourse stewards on the day have with no power to amend the result, which has been referred to the BHA.
The British Horseracing Authority issued a statement which read.
"The incident at Yarmouth has been referred to the BHA's head office in order that we can carry out an investigation, in accordance with our rules. Since we introduced the microchipping identification system an incident such as this is, as far as we are aware, unprecedented.
"The issue had not been established until after the result had been made official. After the weighed-in has been declared on the racecourse, the result cannot be amended by the stewards."
"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."
