Simplify the following text for a Grade 7 native English-speaking person.
Original: An agnatic relative of William III , John William Friso of Nassau , who also by female line descended from William the Silent , was designated the heir to the princes of Orange in the Netherlands by the last will of William III .
Simplified: John William Friso of Nassau was chosen as the heir to the princes of Orange in the Netherlands by the last will of William III . John William Friso was also related to William the Silent through the female line .