owner of the palace was Jerzy Sebastian Lubomirski—Grand Crown Hetman and Crown Chancellor, and later the leader of a rebellion against the king—who bought the palace from Aleksander Koniecpolski. In 1674 the palace became, for the next 144 years, the property of the Radziwiłł family. It was bought from descendants of Jerzy Sebastian Lubomirski—Stanisław Herakliusz Lubomirski and Hieronim Augustyn Lubomirski—by Michał Kazimierz Radziwiłł of the Nieśwież–Ołyka line, whose wife Katarzyna was a sister of King Jan III Sobieski. After her death, her son Karol Stanisław Radziwiłł I began renovation of the palace and tidied up its surroundings. He entrusted this task to the king's architect, Augustyn Locci. The next-to-last heir in tail of Nieśwież and Ołyka was Karol Stanisław "Panie Kochanku" Radziwiłł, Voivode of Vilnius, son of Michał Kazimierz "Rybeńko" Radziwiłł. He had inherited huge estates from his father and uncle which made him the wealthiest magnate in Poland in the second half of the 18th century, and one of the richest men in Europe. He leased out the palace to Franciszek Ryx to house a theater which staged plays and threw masked balls. During the Four-Year Sejm of 1788–1792, he invited all the members of the four deliberating estates to dine there daily. Two meals were served every day: breakfast before the day's session, for 300 people, and dinner after the session. One of the most impressive feasts given by him was on St. Catherine's Day, November 25, 1789, the 25th anniversary of King Stanisław August's coronation, and commemorating the Union of Lithuania with the Polish Crown. Four thousand guests were invited, and the feast cost over 2 million zlotys. On the night of May 2–3, 1791, a conspiratorial group of members of the Four-Year Sejm who were bent on saving the Commonwealth met at the palace to strategize means to secure the adoption, next day, of the May 3rd Constitution. This document is called "the first constitution of its kind in Europe" by historian Norman Davies. Karol Stanisław Radziwiłł II died a sick and blind man at age 56. His property was inherited by Dominik, son of his half-brother Hieronim. Dominik, who had been wounded at the Battle of Hanau, died heirless on November 11, 1813. The line of the Nieśwież–Ołyka heirs in tail died out with him. In 1818 the palace became the seat of the Viceroy of the Polish (Congress) Kingdom (when it acquired the name