William was the heir presumptive to the Prussian throne. His eldest brother, Prince Frederick William, was childless, and it was expected that William would eventually inherit the throne. Because of this, he was also expected to marry a princess within his rank and have children. Unfortunately, Elisa was not that princess. Although her mother was a Prussian princess by birth, she descended into her husband's rank as a mere Polish noble. Thus, Elisa was considered to be not royal enough to marry the heir to the Prussian throne.