Background
He was the eldest son of Konrad III the Red and his third wife Anna, a daughter of Mikolaj Radziwiłł the Old, Voivod of Vilnius and the first Grand Chancellor of Lithuania.
He was the eldest son of Konrad III the Red and his third wife Anna, a daughter of Mikolaj Radziwiłł the Old, Voivod of Vilnius and the first Grand Chancellor of Lithuania.
Despite this, Anna Radziwiłł retained the real power in Masovia until her death in 1522. In 1519, fulfilling his duties as Polish vassals, Stanisław and Janusz III intervened in the Polish-Teutonic War, sending auxiliary troops to the Polish King, and in the winter of 1519-1520 they personally captured several town in Masuria. The wedding never took place.
One year later, and likely for his dissolute lifestyle, Stanisław died on 8 August 1524, probably shortly before Noon.
He was buried at Saint John"s Archcathedral, Warsaw. The main suspect was a Płock lady called Katarzyna Radziejowska, who after being seduced and abandoned by both princes, in revenge she could poisoned firstly Anna Radziwiłł, then Stanisław and finally Janusz III. Declared guilty, she and her supposed accomplice where tied naked to poles and beaten for hours, and finally burned alive.
The hurry where the sentence was carried caused even more suspicions that in fact the real instigator of the crimes was Queen Bona. The controversy was so intense that King Sigismund I, in order to clarify the matter once and for all, ordered an investigatation, as a result of which was declared a special edict on 9 February 1528 who ruled that the princes "weren"t victims of a human hand, but was the will of the Almighty Lord that caused their deaths".
According to January Długosz, the real cause of the death of both princes could be an inherited disease of the Masovian princes: tuberculosis.