Siemowit III, Duke of Masovia Polish nobleman (1314–1381) Parents Maria of Galicia Trojden I, Duke of Masovia Children Euphemia of Masovia Janusz I of Warsaw Siemowit IV Stanisław Siemowit of Masovia Margaret of Masovia Henry of Masovia Siblings Bolesław Jerzy of Mazovia Casimir of Masovia Eufemia of Masovia Partners Euphemia of Opava Anna von Münsterberg