‘A special racehorse.’ Prized stallion Uncle Mo dies after leg injury, surgery.

Uncle Mo, a horse whose brilliance on the racetrack was never fully realized before his legendary career as a stallion, died Thursday at age 16.

“We’re all still in shock,” Coolmore America manager Dermot Ryan told BloodHorse. “He will be greatly missed by everyone here.”

Owner Mike Repole posted on X that Uncle Mo underwent surgery Wednesday after suffering an injury to his left front foreleg.

“Unfortunately, this morning the recovery process was too much for him to endure,” Repole said after Uncle Mo was euthanized.

“The Repole Stable family, Todd Pletcher family and the entire Coolmore family are heartbroken,” Repole continued. “Uncle Mo was so much more to me than a champion and iconic stallion — he was and always will be a part of my family.”

Uncle Mo won his first four career races, including a dominant 4¼-length win in the 2010 Breeders’ Cup Juvenile that led to his winning the Eclipse Award for champion 2-year-old colt. However, he missed the entire Triple Crown series in his 3-year-old season battling what was called a stomach ailment when he was scratched the day before the 2011 Kentucky Derby as the 9-2 second choice.

Uncle Mo, trained and ridden by Hall of Famers Pletcher and John Velazquez, respectively, was later diagnosed with a liver disease but bounced back to race three more times in 2011 before being retired.

As a stallion, Uncle Mo was able to deliver the results his health never fully allowed him to achieve on the track.

Even at age 16, his stud fee was recently advertised at $125,000 for the 2025 breeding season a number well-earned through the siring of more than 100 stakes winners through the years.

His offspring included Kentucky Derby winner Nyquist, Belmont Stakes champion Mo Donegal, two-time Breeders’ Cup winner Golden Pal, Stephen Foster and Louisiana Derby winner Kingsbarns, and Pacific Classic victor Arabian Knight.

Uncle Mo’s stud fee peaked at $150,000 in 2017, according to BloodHorse, and never dropped below $125,000 again.

“Uncle Mo is the patriarch of Repole Stable,” Repole’s statement said. “There will never be another horse that makes me feel or will impact my life the way that Uncle Mo has. … Thank you Uncle Mo for fulfilling my childhood dreams of owning a special racehorse.”