Roman (or Boris) was the son of Vladimir I, Grand Duke of Russia; Olga was his great-grandmother. After the death of Vladimir I, Boris and his youngest brother Gleb were murdered in the turmoil and disputes over the heir to the throne. Historically, the question of guilt is unresolved. According to church tradition, Boris’ half-brother Svyatopolk seized the capital Kiev after the death of his father and had Boris killed, who – on a military campaign against the rebellious Turkish people of the Pechenegs – had the largest force. Immediately afterwards, he arranged for the murder of Boris’ youngest brother Gleb. Sviatoslav, another brother, had fled to the Carpathians, but he also died under the knives of his henchmen. Of the brothers, only Yaroslav, who resided in Novgorod – today’s Nizhny Novgorod – escaped with his life. In 1019, Yaroslav defeated the army of Svyatopolk and chased him to the Tatras, where he died disgracefully. Yaroslav, later called the Sage, thus avenged the murder of his brothers. As early as 1050, the veneration of Boris and Gleb began in the Kiev ruling house.
Joachim Schäfer: Article Boris, from the Ecumenical Dictionary of Saints – https://www.heiligenlexikon.de/BiographienB/Boris.html