In order to deal with the issue, Constantin Şerban allied himself with the Transylvanian Prince George II Rákóczi, including himself in the latter's plans for emancipation from Ottoman rule.

In 1657, the Porte deposed him; Constantin Şerban went on to fight alongside Rákóczi, managing to upset Ottoman presence in Moldavia and briefly occupying the throne in Iaşi, at two different moments (in 1659 and 1661).

Paul of Aleppo documents the derelict state of Wallachia during the Ottoman intervention, including an account of the rural population fleeing for the Transylvanian Alps ("where the Wallachians were accustomed to take refuge in time of need").

In 1656, the Prince ordered the building of the Bucharest Metropolitan Cathedral (today: Patriarchal), partly modeled on the Curtea de Argeş Monastery – but larger and more austere.

In his honour, the church was given the patronage of Eastern Orthodox Saints Constantine (his namesake) and Helena.