Background
She was the third daughter of Siemowit IV, Duke of Masovia, by his wife, Alexandra, daughter of Algirdas, Grand Duke of Lithuania and sister of King Władysław II Jagiełło of Poland.
She was the third daughter of Siemowit IV, Duke of Masovia, by his wife, Alexandra, daughter of Algirdas, Grand Duke of Lithuania and sister of King Władysław II Jagiełło of Poland.
According to the Chronicle of January Długosz, Euphemia had a great and natural charm, and because of this she was also known as Ofka. Because Euphemia and Bolesław I were related in the third degree of consanguinity, a Papal dispensation was needed for the union, which was granted on 27 January 1412. The wedding took place ten months later, on 20 November, probably in the town of Wiślica.
Alexandra of Cieszyn (ca 1412 - d aft 6 October 1463), married to László Garai, Palatine and Ban of Macsó.
Wenceslaus I, Duke of Cieszyn (1413/18 - 1474). Władysław, Duke of Głogów (ca 1420 - 14 February 1460).
Przemysław II, Duke of Cieszyn (1422/25 - 18 March 1477). Bolesław II, Duke of Cieszyn (ca 1425/28 - 4 October 1452).
On 29 November 1442 the co-Dukes of Cieszyn made a formal division of their domains.
However, the unity of the Duchy was maintained during Euphemia"s lifetime.