John Sigismund, originally Roman Catholic, converted to Lutheranism before the end of 1562. However, debates between Lutheran and Calvinist theologians continued. John Sigismund appointed his court physician, Giorgio Biandrata (who as an Anti-Trinitarian did not share either the Lutheran or the Calvinist view) to head a synod to reconcile the Lutheran and the Calvinist clergymen, but their differences proved insuperable in April 1564. The Diet acknowledged the existence of a separate Calvinist denomination in June. John Sigismund also adopted Calvinism and made Ferenc Dávid his court preacher.