Battlestar Galactica (2004)

S01E06 Litmus

A fresh Doral model, a Cylon who once acted as the Galactica's public-relations officer, covertly infiltrates the ship and detonates himself, resulting in the deaths of three individuals. In the aftermath, Commander Adama and President Roslin are forced to reveal a shocking truth that has been kept hidden from all but a few: Cylons now possess human appearances.