John of the Lithuanian Dukes

John of the Lithuanian Dukes (Jan Ochstat de Thelnicz, Lithuanian: Jonas iš Lietuvos kunigaikščių, Polish: Jan z Książąt Litewskich; 8 January 1499 – 18 March 1538) was Bishop of Vilnius (1519–36) and of Poznań (Posen) (1536–38). He was the bishop when Protestantism was making the first inroads into the Grand Duchy of Lithuania and took the first steps in combating it. John was an illegitimate son of Sigismund I the Old, King of Poland and Grand Duke of Lithuania, and his mistress Katarzyna Telniczenka.

John was born in 1499, well before Sigismund's first marriage to Barbara Zápolya in 1512. In July 1510, John's father received papal dispensation to remove defectus natalium, recognize him as a legitimate son, and ennoble him. John was granted the title "of the Lithuanian Dukes" around 1514 and used a version of the Lithuanian coat of arms. John became canon in Kraków in 1510 and in Poznań in 1516. John was a student at Kraków Academy and University of Bologna. In 1519, at the age of 21, John was nominated Bishop of Vilnius by his father. Long-term canon of Vilnius John Filipowicz was nominated to become Bishop of Kiev.Pope Leo X confirmed the nomination even though John was not yet ordained as priest (it happened only in 1531) and the Third Council of the Lateran required bishops to be at least 30 years of age. John was accompanied by his mother who interfered in diocesan affairs. John and his mother faced a lot of opposition in Vilnius; he was even physically attacked and injured by Stanisław, son of Grand Chancellor Mikołaj II Radziwiłł. That prompted the pope to place John under the tutelage of Bishops of Kraków and Lutsk.

...
Wikipedia