Upon the death of his kinsman Albert I, Duke of Prussia in 1568, the Duchy of Prussia was inherited by the latter's underage son Albert Frederick. John George's father was a co-inheritor of the Duchy of Prussia. In 1577 the Brandenburg electors became co-regent with Duke Albert Frederick of Prussia.
uPoN the deatH of hiS kInsman AlbeRT i, dUKe OF PrUssia in 1568, The ducHy Of prussia was iNhEriTED bY tHe LaTter's UnDEraGe soN albert fREderIck. JOHn gEorgE'S Father WaS a CO-InhEritor Of ThE duchY Of PRussiA. In 1577 the BrandeNBuRg elecTOrs beCame CO-reGent WItH dUke aLbert fReDErick of pRUssIA.