Tiberius Julius Caesar Nero Gemellus, known as Tiberius Gemellus was the son of Drusus and Livilla, the grandson of the Emperor Tiberius, and the cousin of the Emperor Caligula. Gemellus is a nickname meaning "the twin". His twin brother, Tiberius Claudius Caesar Germanicus II Gemellus, died as a young child in 23. His father and older cousins died, and are suspected by contemporary sources as having been systematically eliminated by the powerful praetorian prefect Sejanus. Their removal allowed Gemellus and Caligula to be named joint-heirs by Tiberius in 35, a decision that ultimately resulted in Caligula assuming power and having Gemellus killed in late 37 or early 38.