Human-Time Lord Meta-Crisis

A Human-Time Lord Meta-Crisis is the term applied to a hybridized organism that combines the traits of a Time Lord and Human. Only two have been known to exist - the "DoctorDonna" and the Meta-Crisis Tenth Doctor. The DoctorDonna had to be reverted to her Human self, as Human brain cannot hold a Time Lord Consciousness so the original Tenth Doctor had to erase Donna's mind. (DW: Journey's End)