In October 37, Caligula fell seriously ill, or perhaps was poisoned. He soon recovered from his illness, but many believed that the illness turned the young emperor toward the diabolical: he started to kill off or exile those who were close to him or whom he saw as a serious threat. Perhaps his illness reminded him of his mortality and of the desire of others to advance into his place. He had his cousin and adopted son Tiberius Gemellus executed – an act that outraged Caligula's and Gemellus's mutual grandmother Antonia Minor. She is said to have committed suicide, although Suetonius hints that Caligula actually poisoned her. He had his father-in-law Marcus Junius Silanus and his brother-in-law Marcus Lepidus executed as well. His uncle Claudius was spared only because Caligula preferred to keep him as a laughing stock. His favourite sister, Julia Drusilla, died in 38 of a fever: his other two sisters, Livilla and Agrippina the Younger, were exiled. He hated being the grandson of Agrippa and slandered Augustus by repeating a falsehood that his mother was actually conceived as the result of an incestuous relationship between Augustus and his daughter Julia the Elder.