Following an illness suffered by Caligula, Gemellus was put to death in late 37 or early 38. Cassius Dio places his death and that of Caligula's father-in-law Marcus Junius Silanus in the events of late 37. Their replacements in the Arval Brethren were not found until 24 May 38. He goes on to explain that Gemellus waited for a chance to benefit from Caligula's illness. According to Philo, Caligula's pretended reason was a conspiracy. Suetonius says that Gemellus took medicine for a chronic cough and that the smell was detected, leading to accusations of taking an antidote for poison. He was ordered by Caligula to commit suicide for which soldiers gave him a sword and had to help him because he is said not to have known how to kill himself with it.