Louis I, Grand Duke of Hesse
In 1776, he became engaged to Sophie Dorothea of Württemberg, eldest daughter of Frederick II Eugene, Duke of Württemberg. The engagement was broken off so that Sophia Dorothea could marry Louis's recently widowed brother-in-law Tsarevich Paul Petrovich, son and heir of Catherine II "the Great", Empress of Russia. He received a monetary compensation when the engagement was broken.
Sophia of Prussia
Sophia and Constantine's marriage was harmonious during the first years. However, faithfulness was not the greatest quality of the "Diadochos" and his wife soon had to deal with his numerous extramarital affairs. Initially shocked by what she saw as a betrayal, Sophia soon followed the example of her mother-in-law and condoned the behavior of her husband. From 1912, however, the couple became noticeably separated. At that time, Constantine began an affair with Countess Paola von Ostheim ("née" Wanda Paola Lottero), an Italian stage actress who had recently divorced from Prince Hermann of Saxe-Weimar-Eisenach; this relationship lasted until Constantine's death.