On 15 March 44 BC Caesar was murdered in Rome by a group of conspirators whose most notable members were Marcus Junius Brutus and Gaius Cassius Longinus. Ptolemy soon followed him in death. An inscription mentioning him as alive was dated at 26 July 44 BC. It has been assumed but remains uncertain that Cleopatra poisoned her co-ruler, with aconite, to replace him with his nephew Ptolemy XV Caesar, her son by Caesar who was proclaimed co-ruler on 2 September 44 BC and whom his mother intended to support as successor of his father.