EXCLUSIVE

Incubus singer Brandon Boyd has been ruthlessly stalking a former "Real World" star -- even threatening to kill her -- so says the former "Real World" star ... but Brandon says B.S.

Svetlana Shusterman from "Real World 17: Key West" got a temporary restraining order against Boyd, claiming Brandon's been stalking her for years ... and recently began threatening her life.

Svetlana filed a police report claiming Brandon had followed her car onto a freeway and yelled through the window that he was going to kill her.

Svetlana says she recently moved to a friends house to evade him, but he tracked her down. She writes, "Every day, I am terrified."

Boyd has been ordered to stay 100 yards away from her pending a court hearing next month.