After the heavy blow dealt to the Bulgarian Empire by the Rus' Prince Svyatoslav I, in 971 the Byzantines, under the pretext of liberating Bulgaria from the Rus', captured the capital Preslav and expelled Svyatoslav's forces from the Balkans. However, following these events, Bulgarian Emperor (Tzar) Boris II was taken hostage to Constantinople by Byzantine Emperor John I Tzimiskes and forced to publicly abdicate his throne. The eastern portion of the Bulgarian Empire was annexed by Byzantium, while the western parts were left to their own devices and came under the control of the four sons of the Bulgarian governor of Sredets (modern Sofia) - count Nikola. The fours sons (David, Moisei, Aron, and Samuil) came to be collectively known by the Byzantines as the "Cometopuli" ("sons of the count"), and would lead Bulgarian resistance to Byzantine subjugation (formally in the name of the captive Boris II).