Gaius Caesar
The deaths of Germanicus' oldest sons elevated his third son, Gaius Caesar (Caligula), to successor and he became "princeps" when Tiberius died in AD 37. Drusus the Younger's son Tiberius Gemellus was summoned to Capri by his grandfather Tiberius, where he and Gaius Caligula were made joint-heirs. When Caligula assumed power, he made Gemellus his adopted son, but Caligula soon had Gemellus killed for plotting against him.