sentences:  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.After the death of their father on 28 October 1503, Stanisław and his younger brother Janusz III inherited his domains but, because they were minors, remained under the regency of their mother.Most of the Masovian inheritance (except Czersk, which had already been given to Konrad III as a hereditary fief in 1495) was seriously threatened by the Kingdom of Poland at the time of Konrad III's death, and was not secured in his sons' hands until 14 March 1504, when by a ruling of King Alexander, the young princes received their whole patrimony as a fief.