John of the Lithuanian Dukes

John was an illegitimate son of Sigismund I the Old, King of Poland and Grand Duke of Lithuania, and his mistress Katarzyna Telniczanka.

In July 1510, John's father received papal dispensation to remove defectus natalium, recognize him as a legitimate son, and ennoble him.

[4] Pope Leo X confirmed the nomination even though John was not yet ordained as priest (it happened only in 1531)[4] and the Third Council of the Lateran required bishops to be at least 30 years of age.

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.

[2][4] John also received papal legate Zacharias Ferrerius sent to investigate canonization of Saint Casimir after a miracle attributed to him during the Siege of Polotsk (1518).

In 1522, he revised the curriculum of the Cathedral School of Vilnius to include rhetoric, dialectics, classical literature, arithmetic, music.

[5] In 1526 or 1527, John called the second diocesan synod which debated three major topics: improper behavior by priests, proper procedures of church services, and establishment of schools.