Complex sentence: Later in the year, he won the Breeders' Cup Mile on the gelding Wise Dan, who went on to become a two-time American Horse of the Year in 2012 and 2013 with Velazquez as his regular rider.
Split into simpler sentences: Later in the year, he won the Breeders' Cup Mile on the gelding Wise Dan. The horse went on to become a two-time American Horse of the Year in 2012 and 2013 with Velazquez as his regular rider.