Middleton was slow to mature and did not run as a two-year-old. In early 1825, however, he performed well in private trial races. Despite never having raced in public, he became the leading fancy for
The Derby and was the subject of much heavy betting for the race, with Lord Jersey and the
Duke of Wellington among the biggest gamblers. and won cleverly, from Rufus, with Hogarth third. Both Jersey and Wellington reportedly claimed over £1,000 in winning bets. In autumn, Middleton was entered in several match races but did not run after either he or his opponent was withdrawn. Middleton began to suffer from
Navicular Disease which caused chronic lameness. It proved impossible to run him again, and he was retired to stud with an unbeaten record. ==Stud career==