US Triple Crown hero Justify has been retired.

He was the 13th winner of the famous classic treble and he has finished his racing career undefeated in six starts, all of them in 2018, with career earnings of $3,798,000. The tally also includes the Grade 1 Santa Anita Derby, and Mike Smith was in the saddle for all bar his debut success.

"Justify had some filling in his ankle, and he is not responding quick enough for a fall campaign," said trainer Bob Baffert. "We all wanted to see Justify run again, but ultimately it is my responsibility to make sure he is perfect. Without 60-90 days, I can't be definite."

The chesnut son of late Ashford Stud stallion Scat Daddy became just the second horse to win the Kentucky Derby having been unraced as a two-year-old when powering through the slop to beat Good Magic at Churchill Downs on the first Saturday in May. The other one was Apollo, in 1882.

Conditions were also wet when he held on to beat Bravazo in the Preakness Stakes at Pimlico two weeks later, but it was on a bright and sunny day in June when secured the classic hat-trick with defeat of Gronkowski in the Belmont Stakes in New York.

Justify was bred by John Gunther – who is also the breeder and owner of Group 1 St James's Palace Stakes winner Without Parole – and is owned by the partnership of WinStar Farm, China Horse Club, Head of Plains Partners and Starlight Racing.