Germanicus, Drusus the Younger was Tiberius' new heir. He received a second consulship in AD 21 and tribunicia potestas (tribunician power) in AD 22. At the same time, Praetorian Prefect Sejanus started to exert considerable influence over the emperor, who referred to Sejanus as Socius Laborum ("my partner in my toils"). Around AD 20, when Sejanus became the first of the equestrian order to hold the praetorship, a senatorial office, his daughter Aelia Junilla was born and swiftly betrothed to Nero's cousin, the boy Claudius Drusus, firstborn son of the future emperor Claudius. At the prospect of a familial bond between the Claudia gens and Sejanus's family, Drusus the Younger is reported by Tacitus to have said of Sejanus in disgust "the grandsons of us Drususes will be his grandsons too". (.) According to Tacitus and Cassius Dio, the Younger Drusus and Sejanus began bickering and entered a feud. Subsequently, Drusus became ill and died of seemingly natural causes on 14 September AD 23. Claudius Drusus also died before reaching adulthood. Ancient sources suggested that the cause of Drusus' death was poison, whereas modern authors like Barbara Levick are more sceptical, suggesting it may have been illness. The death of the Younger Drusus left no immediate threat to Sejanus. Ultimately, his death elevated Nero and his brother Drusus to the position of heirs. In effect, this led to the formation of factions, with one faction around Nero and Drusus and their mother Agrippina and the other faction linked to Sejanus. While the full extent of Sejanus' power at this point is uncertain, it can be noted that Sejanus was not allowed to marry Livilla (Drusus the Younger's widow) and was thus denied entry into the imperial family. In the Senate, Sejanus encountered little opposition from the senators, but Tiberius expressed displeasure in the Senate, in AD 24, at the public prayers which had been offered for Nero and his brother Drusus' health. In AD 28, the Senate voted that altars to Clementia (mercy) and Amicitia (friendship) be raised. At that time, Clementia was considered a virtue of the ruling class, for only the powerful could give clemency. The altar of Amicitia was flanked by statues of Sejanus and Tiberius. By this time, Sejanus' association with Tiberius had reached the point where members of Roman society were erected statues in his honour and gave prayers and made sacrifices in his honour.