Iaroslav was the second son of
Sviatopolk Iziaslavich (who was the youngest son of
Iziaslav I Iaroslavich,
Grand Prince of Kiev). Iziaslav fled to Poland after his brothers,
Sviatoslav Iaroslavich and
Vsevolod Iaroslavich, dethroned him in 1073. Sviatopolk accompanied his exiled father. Historian Márta Font proposes that Sviatopolk had most probably fathered children by the time he left Kievan Rus'. One "
Gerasclauus, the son of the king of the
Ruthenians" was listed among the witnesses of the deed of foundation of the
Somogyvár Abbey in 1091. The document also recorded that
Gerasclauus was the son-in-law of
Ladislaus I of Hungary. Font associates
Gerasclauus with Iaroslav, because Iaroslav's good relationship with the Hungarian kings is well-documented. She says that Iaroslav most probably married Ladislaus I's daughter in the early 1090s. In 1097, his father sent Iaroslav to Hungary to persuade
Coloman, King of Hungary to support him. ==Prince==