Kitasan Black, a five-time Grade One race winner, will retire after the Arima Kinen in December, the stallion's trainer Hisashi Shimizu said on Friday.
"(Kitasan Black's) owner (Saburo Kitajima) decided that he would retire this year after running the autumn Tenno-sho, the Japan Cup and the Arima Kinen," Shimizu said in a Japan Racing Association statement.
"He has a lot of fans so there will be disappointment but he will be put out to stud at a stallion station while he is still full of life. That's his next important job."
Kitasan Black, by Black Tide out of Sugar Heart, won the 2015 Kikka-sho, and in 2016 won the spring Tenno-sho and the Japan Cup.
In April, the 5-year-old won the Osaka-hai, the newest G1 race on the JRA calendar, and then became just the fourth horse to defend the spring Tenno-sho title, while breaking Deep Impact's 11-year-old record time.