Euphemia of Masovia Bef 1341 - 21 May 1418/9 Dec 1424 Parents Euphemia of Opava Siemowit III, Duke of Masovia Children Jadwiga of Opole Katharina of Opole Siblings Henry of Masovia Margaret of Masovia Janusz I of Warsaw Siemowit IV Stanisław Siemowit of Masovia Partners Vladislaus II of Opole