Sad news for Stephan Bonnar ... the UFC legend's family says its Nevada home was destroyed in a fire this week.
TMZ Sports has learned ... the Henderson Fire Dept. received a call for a residential fire at 2:40 PM on Monday ... and when help arrived on the scene, fire and smoke were visible from outside the home.
Due to high winds and the closeness to the neighboring homes, the first responders called on the Clark County FD for backup in order to get the blaze out.