Given the rationale, provide a reasonable question and answer. Step-by-step reasoning process: The relevant information to answer the above question is: In the history of the Triple Crown, 13 horses have won all three races: Sir Barton (1919), Gallant Fox (1930), Omaha (1935), War Admiral (1937), Whirlaway (1941), Count Fleet (1943), Assault (1946), Citation (1948), Secretariat (1973), Seattle Slew (1977), Affirmed (1978), American Pharoah (2015), and Justify (2018).
 The question and answer:
In the history of the Triple Crown, 13 horses have won all three races: Sir Barton (1919), Gallant Fox (1930), Omaha (1935), War Admiral (1937), Whirlaway (1941), Count Fleet (1943), Assault (1946), Citation (1948), Secretariat (1973), Seattle Slew (1977), Affirmed (1978), American Pharoah (2015), and Justify (2018). As of 2018, American Pharoah and Justify are the only living Triple Crown winners.

What was the last horse to win the triple crown?
The answer is Justify ( 2018 )