Reggie Miller just announced his dad has passed away ... and the NBA legend says he's completely heartbroken over the death.
"This HURTS," the former Indiana Pacers star said on his social media page on Monday.
"The man who bought me my first set of baseball cleats, first basketball, who taught me to drown out all the outside noise and FOCUS is now and will forever be my guardian angel."
Miller's father, Saul, had five kids with his wife, Carrie -- including Reggie and Cheryl Miller, a former basketball star herself.