因胡安娜的哥哥，姐姐及姐姐之子皆先于伊莎贝拉女王死掉，胡安娜便成为西班牙卡斯蒂利亚王国唯一之王位继承人。
Antecedent to the queen 's death , Juana 's older brother , older sister , and older sister 's son had all become deceased leaving Juana the heir to the throne of Castile .
卡斯蒂利亚王国