Clutch Disc Exploded!

[Ken MA]

Driving the 30 Town Sedan to the Belltown Motorcar Meet and suddenly I was coasting. Thought the car had slipped into neutral but would not engage any gear. After the tow home I opened the inspection plate and found the clutch disc demolished with the springs at the bottom of the bell housing. The disc was new 3000 miles ago when i had the engine rebuilt. My concern now is why did this happen and what can be done to prevent it from happening again. I would appreciate any input.