Her paternal grandparents were Trojden I of Masovia and his wife Maria, daughter of Yuri I of Galicia and Euphemia of Kuyavia.
Therefore, this marriage was a very important alliance and it had been hoped it would possibly introduce the Masovian blood into the Polish royal family.
Casimir had been married once before to Johanna of Lithuania, who had died the year before Margaret's marriage, without any children.
They had a couple of children who died young before Anna gave birth to a healthy son, Henry.
[2][better source needed] They were married for eight years and had two children: Margaret's date of death is disputed but it is believed that she died on either 14 May 1388 or 4 April 1396.