In the spring of 22, his father Drusus received "tribunicia potestas" (tribunician power) from the Senate, a clear sign that Drusus was Tiberius' heir. However, the following year marked a turning point for his father when his dispute with the powerful praetorian prefect Lucius Aelius Sejanus reached a critical point. In the account of Tacitus, Sejanus began plotting against Drusus to secure his position. On 14 September 23 his father died from what passed as natural causes. According to Cassius Dio and Tacitus, his father was poisoned by his wife Livilla at the behest of Sejanus. The exact cause of the feud is unknown.