While it was officially Drusus who was the heir to Tiberius, in practice, it was the Praetorian prefect Sejanus who was the second man in the empire. As early as AD 20, Sejanus had sought to strengthen his ties to the imperial family by betrothing his daughter Junilla to the son of Claudius, Claudius Drusus. At the time the girl was only 4 years old but the marriage was prevented when the boy accidentally died a few days later of asphyxiation. Regardless, his ambition to further expand his power was clear.