John IV originally recognised the suzerainty of the Byzantine Emperor.
In 999, he was captured and taken a prisoner first to Capua, then back to Germany by Otto III, the Holy Roman Emperor, who had just visited Saint Nilus the Younger in Gaeta.
During his absence, Naples seems to have continued in allegiance to the Greeks, though it was technically governed by Adhemar of Spoleto.
In 1002, John reappears in his duchy, probably released by Otto's successor, Henry II.
A second daughter is recorded unnamed by Amatus of Montecassino as having been widowed by the count of Gaeta and remarrying soon after to Ranulf Drengot, the Norman count of Aversa.