When Tiberius died on 16 March AD 37, Caligula was well-positioned to assume power, despite the obstacle of Tiberius’s will, which named him and his cousin Tiberius Gemellus as joint heirs. Caligula ordered Gemellus killed within his first year in power. Backed by Naevius Sutorius Macro, Caligula asserted himself as sole princeps, though he later had Macro disposed of as well.. Following Gemellus' death, Caligula marked his brother-in-law, Marcus Aemilius Lepidus, husband of his sister Julia Drusilla, as his heir. However, after Drusilla's death, Lepidus was accused of having affairs with Caligula's other sisters Agrippina the Younger and Julia Livilla and he was executed. He had previously had Drusilla's first husband Lucius Cassius Longinus killed and upon the death of Agrippina's husband Gnaeus Domitius Ahenobarbus, he seized his inheritance.