vytautas' uncle algirdas had been grand duke of lithuania until his death in 1377. algirdas and vytautas' father kęstutis had ruled jointly in the form of diarchy, with algirdas governing the east and kęstutis the west, primarily responsible for defense against the teutonic order. algirdas was succeeded by his son jogaila, and a struggle for power ensued. in 1380, jogaila signed the secret treaty of dovydiškės with the teutonic order against kęstutis. when kęstutis discovered this in 1381, he seized vilnius, imprisoned jogaila, and made himself grand duke. however, jogaila escaped and raised an army against kęstutis. the two sides confronted each other but never engaged in battle. kęstutis was ready to negotiate, but he and vytautas were arrested and transported to kreva castle. one week later, kęstutis was found dead. whether he died of natural causes or was murdered is still a matter of debate.