Just over a month after he became the 13th American Triple Crown winner in horse racing history, Justify has been retired because of a problematic ankle, the Associated Press reported Wednesday.

Hall of Fame trainer Bob Baffert had been angling to run Justify, whose dominance made him a heavy favorite in the 2018 Kentucky Derby, at least once more this summer, and perhaps in November's Breeders' Cup Classic at Churchill Downs. But he was "taken out of training earlier this month," according to the AP, "because of swelling in his ankle" -- an issue that had Baffert and the horse's owners hesitant to proceed.

"The timing is bad for another start in 2018, and therefore, we have to retire him," said WinStar Farm's Elliott Walden, one of Justify's owners, per the AP. "Like American Pharoah, we can't take the risk of running Justify as a 4-year-old. We all wanted him to finish his career in the Breeders' Cup Classic, but it was not meant to be."

That means Justify, who earned almost $3.8 million in his career, will retire having won all six of his starts. The highly reputed specimen famously began his Triple Crown run by snapping the Apollo Curse, becoming the first horse since 1882 to win the Kentucky Derby after not racing as a 2-year-old. Wins at the Preakness and Belmont Stakes then made him the second American Triple Crown champion of the last four years -- and just the 13th of all time.

Amid his roaring 2018 success, Justify's breeding rights were reportedly sold for more than $60 million -- and possibly up to $85 million -- by WinStar Farm, China Horse Club and SF (Soros Fund) Racing. According to the AP, Walden said it's possible a sale of the breeding rights will be finalized, but he wouldn't confirm a deal has already been struck, saying it would have to come at a later date.