Regret became the first filly to win the Kentucky Derby in 1915.
Bred and owned by Harry Payne Whitney, Regret was trained by James G. Rowe Sr. She entered the Derby unbeaten after winning all three of her previous starts, including important races for two-year-olds.
Regret won the Derby at Churchill Downs by two lengths despite a slow early pace and muddy conditions. Her victory was especially notable because fillies were rarely entered against colts in major American races at the time.
Regret remained the only female Kentucky Derby winner for 65 years. Genuine Risk became the second in 1980, followed by Winning Colors in 1988. Regret was inducted into the National Museum of Racing and Hall of Fame in 1955 and is widely regarded as one of the most important American racehorses of the early 20th century.