As of 2019, which horse won the American Triple Crown that did not race as a two-year-old?

Justify (foaled March 28, 2015) is a retired American Thoroughbred racehorse who is the thirteenth and most recent winner of the American Triple Crown, accomplishing the feat by winning the Kentucky Derby, Preakness Stakes, and Belmont Stakes in 2018.

He first attracted attention with a win in his first start on February 18, 2018, followed by two more victories, including the Grade I Santa Anita Derby, to qualify for the 2018 Kentucky Derby. Justify then won that race, the 2018 Preakness Stakes, and the 2018 Belmont Stakes to win the Triple Crown. He was retired undefeated several weeks after the Belmont, thereby becoming the only American Triple Crown winner who never lost a race in his career.

Justify is only the second horse to win the American Triple Crown with an undefeated record, following Seattle Slew. Justify is descended from Seattle Slew, Secretariat, Count Fleet, War Admiral, Omaha, and Gallant Fox, all of whom also won the American Triple Crown. He is also a descendant of English Triple Crown winner Nijinsky. Of the 13 American Triple Crown winners, Justify is the first who did not race as a two-year-old.