The vast expanses of the South Pacific Ocean have, until recently, concealed the identity of the world's rarest whale, the spade-toothed beaked whale (Mesoplodon traversii). Based on the scarcity of records and the total absence of previous sightings, this species is the least known species of whale and one of the world’s rarest living mammals. Two individuals of this species, previously known from only two skull fragments and a mandible, were recently discovered beachcast in New Zealand. Although initially misidentified, we have used DNA analysis to reveal their true identity. We provide the first morphological description and images of this enigmatic species. This study highlights the importance of DNA typing and reference collections for the identification of rare species.