Throughout his life Karol Stanisław Radziwiłł lived mostly in the Nieśwież area and often visited his numerous estates in the Eastern Borderlands of the Commonwealth.
His parents always believed that he would marry young, but Karol had no interest in relationships and love.
In 1752 Karol's father, Michał Kazimierz Radziwiłł, desperately asked if Isabella Czartoryska would marry his son, but Isabella's father, August Czartoryski, refused believing that the couple was too young and undisciplined.
Soon after, Michał Kazimierz began negotiations with Frederick William, Margrave of Brandenburg-Schwedt, and proposed a marriage between his eldest daughter and his son.
Prussian King Frederick II the Great agreed to the proposition as the head of the House of Hohenzollern, however, demanding in return Michał's support for the unfavorable Prussian policy.
Eventually the Margrave refused as his daughter, a strong, patriotic, young woman with anti-Polish sentiment refused to convert to Catholicism, the state religion of the Polish-Lithuanian Commonwealth.

Later that year, Michał Kazimierz suggested that his son marries Maria Lubomirska, the only daughter of Governor of Bolimów, Jan Kazimierz Lubomirski and his wife Urszula Branicka, the sister of famous and wealthy Hetman Jan Klemens Branicki.
Karol himself, was more interested in marrying Teofila Potocka, the daughter of Stanisław Potocki, Voivode of Kiev, and was reluctant to marriage with Maria, but – in this case having the support of his mother – the father after his wife's death (May 23, 1753) led to the engagement, and soon after to the wedding (23 October 1753 in Mościska).
The marriage from the beginning was unfortunate, mostly caused by the rivalry of the two families.
In 1756, in Lwów, Michał Kazimierz sought to annul the marriage in order to preserve his young son's good mental health and strength.
The process continued for several years and, according to Matuszewicz, the dispute concerned only money matters.
Eventually Michał Kazimierz asked the Primate of Rome for help and on November 5, 1760, the Vatican annulled the marriage.
On the basis of the judgment Radziwiłł was forced to pay Lubomirska 228,000 złotys as compensation for the time and the maintenance of marriage.
This tense situation between the two houses, however, brought some good aspects, as from that day Hetman Branicki became a close friend and supporter of the Radziwiłł family.
Throughout his life Karol Stanisław Radziwiłł lived mostly in the Nieśwież area and often visited his numerous estates in the Eastern Borderlands of the Commonwealth. His parents always believed that he would marry young, but Karol had no interest in relationships and love. In 1752 Karol's father, Michał Kazimierz Radziwiłł, desperately asked if Isabella Czartoryska would marry his son, but Isabella's father, August Czartoryski, refused believing that the couple was too young and undisciplined. Soon after, Michał Kazimierz began negotiations with Frederick William, Margrave of Brandenburg-Schwedt, and proposed a marriage between his eldest daughter and his son. Prussian King Frederick II the Great agreed to the proposition as the head of the House of Hohenzollern, however, demanding in return Michał's support for the unfavorable Prussian policy. Eventually the Margrave refused as his daughter, a strong, patriotic, young woman with anti-Polish sentiment refused to convert to Catholicism, the state religion of the Polish-Lithuanian Commonwealth.
Later that year, Michał Kazimierz suggested that his son marries Maria Lubomirska, the only daughter of Governor of Bolimów, Jan Kazimierz Lubomirski and his wife Urszula Branicka, the sister of famous and wealthy Hetman Jan Klemens Branicki. Karol himself, was more interested in marrying Teofila Potocka, the daughter of Stanisław Potocki, Voivode of Kiev, and was reluctant to marriage with Maria, but – in this case having the support of his mother – the father after his wife's death (May 23, 1753) led to the engagement, and soon after to the wedding (23 October 1753 in Mościska). The marriage from the beginning was unfortunate, mostly caused by the rivalry of the two families. In 1756, in Lwów, Michał Kazimierz sought to annul the marriage in order to preserve his young son's good mental health and strength. The process continued for several years and, according to Matuszewicz, the dispute concerned only money matters. Eventually Michał Kazimierz asked the Primate of Rome for help and on November 5, 1760, the Vatican annulled the marriage. On the basis of the judgment Radziwiłł was forced to pay Lubomirska 228,000 złotys as compensation for the time and the maintenance of marriage. This tense situation between the two houses, however, brought some good aspects, as from that day Hetman Branicki became a close friend and supporter of the Radziwiłł family.
Karol Stanisław Radziwiłł (1734–1790)