Tiberius Gemellus
Born Tiberius Julius Caesar Nero in AD 19. He was the son of Drusus and Livilla, the grandson of Tiberius, and the cousin of Gaius Caligula. Gemellus is actually a nickname, meaning "the twin". His twin brother, Tiberius Germanicus Caesar, died in infancy.Gemellus' father Drusus died mysteriously when Gemellus was only four. It is believed that Drusus died at the hands of the Praetorian Prefect, Sejanus. His mother Livilla was put to death because she had been plotting with Sejanus to overthrow Tiberius, and also because she may have poisioned her husband.
Not much is known about Gemellus' life, as he was largely ignored by most of the Imperial family. So much so that one of the major landmarks of his youth, the toga virilus wasn't celebrated until he was eighteen. The normal age to celebrate this is fourteen years.
At the age of twelve Gemellus was summoned to the island of Capri where Tiberius lived, along with his cousin Caligula. Tiberius made both Caligula and Gemellus joint-heirs, but it was clear that Tiberius favored Caligula over his own grandson. Livilla had been Sejanus' lover for a number of years before their deaths, and many figured that Gemellus was really Sejanus' son.
Tiberius died March 16, 37, and Caligula became Emperor. Not long afterwards, Caligula made Gemellus his adopted son. These friendly gestures towards Gemellus would be short lived. He would be killed on Caligula's orders in late 37 or early 38, for supposedly plotting against Caligula while the Emperor was ill.
Unfortunately, little has been written about Gemellus. Most of the information we know about him has been connected to material about Caligula.