The Brujah Antediluvian, whose name has been obscured forever, is said to have been slain by its childe, Troile, duribg the time of the First City. Presumably Troile did not diablerize her founder, for there is no record of Troile assuming the powers of her progenitor.
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Ancient only faked its death, for whatever reason. It's even possible that Troile was the true name of [Brujah] or maybe Troile never existed.