Alexander Jagiellon died in August 1506 and was succeeded by his brother
Sigismund I. Even before Alexander's death, Zabrzeziński renewed the rivalry and spread rumours that Glinski planned to poison Alexander and even hoped to seize the throne himself. Such rumours were effective: Glinski lost his privileges and titles, while his brother Ivan lost
Kiev Voivodeship. As his trial was postponed and Sigismund I travelled to Poland to settle his coronation as King of Poland, Glinski, and his relatives began an armed rebellion against Sigismund I. On 7 February 1508, Glinski attacked
Hrodna and decapitated Zabrzeziński. His men then unsuccessfully attacked
Kaunas Castle in an attempt to liberate imprisoned
Sheikh Ahmed, the deposed Khan of the
Great Horde. He then planned but never began an attack on
Vilnius. Glinski proclaimed himself a defender of the discriminated
Eastern Orthodox believers and envisioned the establishment of the Duchy of Boristen (after
Borysthenes, the ancient Latin name for the
Dnieper River) with capital in
Smolensk. Glinski's rebellion gained limited support among Orthodox nobility and became intertwined with the
Muscovite–Lithuanian War of 1507–1508. Despite support from the
Grand Duchy of Moscow, Glinski failed to capture
Minsk,
Slutsk,
Orsha,
Mstsislaw,
Krychaw. By 1508, Glinski retreated to Moscow and pledged allegiance to
Vasili III of Russia. ==In Moscow's service==