The intervention in the Kievan succession crisis of 1015–1019 by the Polish ruler Bolesław Chrobry en.wikipedia.org/wiki/Boleslaw...
was an episode in the struggle between Sviatopolk I Vladimirovich ("the Accursed") and his brother Yaroslav ("the Wise") for the rulership of Kiev and Kievan Rus'. It occurred when Sviatopolk's father-in-law Bolesław, ruler of Poland, intervened on Sviatopolk's behalf.
When Felix first met the Rus siblings ^^
(The big guys are Lech - father of Poland, and Rus (Kievian Rus)- Father of Ukraine, Russia and Belarus)