In 1630 he accompanied Gustavus into Germany, in the Thirty Years' War and in 1631 was appointed colonel of "the yellow regiment," the king's world-renowned life-guards, at the head of which he captured the castle of Würzburg on October 8, 1631. Brahe took part in the long duel between Gustavus and Wallenstein around Nuremberg as general of infantry, and commanded the left wing at Lützen on November 6, 1632, where he was the only Swedish general officer present. At the very beginning of the fight he received a gunshot wound to his left knee so severe that he had to retire from the battle. After the fighting ended Brahe travelled to Naumburg to recuperate but his condition deteriorated over the next few weeks and he finally died on November 21, 1632 at the age of 28.