Yes, it happens to the best of us. Mine broke in 2013:
Prior to this, I was hearing a creaking noise coming from the seat tube. I thought it might be a loose seat post or saddle, so I tightened the bolts - not knowing I was hastening the failure.
As I recall, it's a M8x1.25 bolt (same diameter & thread as many MTB stem clamp bolts).
Glad you are uninjured - from experience, the feeling of not having your saddle under you anymore can be unnerving.