In 1772, her son and heir, Paul, turned eighteen. Paul and his adviser, Panin, believed he was the rightful tsar of Russia, as the only son of Peter III. His adviser had also taught him that the rule of women endangered good leadership, which was why he was so interested in gaining the throne. Distracting him, Catherine took trouble to find Paul a wife among the minor princesses of the Holy Roman Empire. She chose Princess Wilhelmina of Hesse-Darmstad, who acquired the Russian name "Natalia Alexeievna"), a daughter of Ludwig IX, Landgrave of Hesse-Darmstadt. The bride's older sister, Frederika Louisa, was already married to the Crown Prince of Prussia. Around this time, Catherine allowed Paul to attend the council in order that he might be trained for his work as Emperor. Wilhelmina died in childbirth on 15 April 1776, three years after the wedding. It soon became even clearer to Catherine that Paul wanted power, including his separate court. There was talk of having both Paul and his mother co-rule Russia, but Catherine narrowly avoided it. A fierce rivalry began between them, as Catherine knew she could never truly trust him and Paul wanted his mother's power.