At first it was part of another Polish fiefdom, the Duchy of Masovia, as in 1388 the king of Poland, Władysław Jagiełło, granted Belz to Siemowit IV, Duke of Masovia, for his recognition of Masovia as a fiefdom of Poland and as a dowry for Siemowit's marriage with Jagiełło's sister, Alexandra.
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