He skillfully took advantage of the alarm of the German Protestants after the Battle of White Mountain in 1620, to stipulate with Bremen's Chapter and Administrator John Frederick, Duke of Schleswig-Holstein-Gottorp, his cousin of second degree, to grant coadjutorship of the See of Bremen for his son Frederick, later crown prince of Denmark (September 1621). Coadjutorship usually included the succession of a See. A similar arrangement was reached in November for the Prince-Bishopric of Verden with its Chapter and Administrator Philip Sigismund. In 1623 "Christian's" son succeeded the late "Philip Sigismund" as Frederick II, Administrator of the Prince-Bishopric of Verden, only to flee the troops of the Catholic League under Count Johan 't Serclaes of Tilly in 1626.