Lithuanian history:

Jaunutis

It appears that Grand Duke Gediminas of Lithuania had not designated his own successor. When Gediminas died suddenly in 1341 at the age of about 66 of unknown causes, all of his sons ruled their own regions except for Jaunutis, his youngest son, who had lived with his father in Vilnius, the capital of Lithuania and the seat of its rulers. Gediminas may have been grooming Jaunutis to succeed him at some time in the future, but in 1341 Jaunutis, who became the default ruler of the Vilnius region, was still too young (in his low 30s), too inexperienced, and could not command the obedience of his brothers. His only support in the family was his brother Narimantas. The Lithuanian state, under military pressure from its neighbors, needed a strong hand at its helm. Witnessing the deteriorating security situation in Lithuania in late autumn of 1345 two of his older brothers, Algirdas and Kęstutis, decided to remove Jaunutis from his position in Vilnius and to rule Lithuania together themselves.

Algirdas and Kęstutis were to bring their forces to Vilnius, and to take over. Since Kęstutis was in nearby Trakai and Algirdas was in far away Vitebsk, Kęstutis got to Vilnius first, took the capital, and captured Jaunutis. The news reached Algirdas on his way to Vilnius in Krėva. When Algirdas reached Vilnius, he offered the Grand Ducal title to Kęstutis, but Kęstutis declined the title saying that Algirdas as his senior should rule in Vilnius as the Grand Duke and that they both would live in peace. Jaunutis was given the rule of Zaslawye (Zaslauje, Iziaslav'l) near Minsk in present-day Belarus. Narimantas was allowed to continue ruling Turov and Pinsk. None of the other brothers challenged the change of leadership in Vilnius. Thus began a unique period of 36 years during which two brothers, Algirdas and Kęstutis, ruled Lithuania jointly in harmony, Algirdas focusing on matters in the east, and Kęstutis focusing on matters in the west. Jaunutis, who became baptized in the Orthodox faith as Ivan, continued to rule in Zaslawye until his death in about 1366. (Click here to read more history.)