After the death of Janusz III of Masovia in 1526, Sigismund succeeded in uniting the Duchy of Masovia and Warsaw with the Kingdom of Poland. There was speculation whether Janusz and his younger brother Stanisław were poisoned by a subject of Queen Bona. The accusations were so pervasive and rampant that Sigismund ordered an investigation, as a result of which a special edict was declared on 9 February 1528 confirming that the Masovian princes died naturally or due to related illness. According to chronicler Jan Długosz, the real cause of the death of both princes could have been inherited tuberculosis.