Diederic went back to serve under Marshal Turenne in Germany, and made the campaign of 1644. He was again taken Prisoner, but soon released; and served in the end of the same campaign. He was detached by the Duke d'Anguien and Marshal Turenne to take Fridelshem and Neudstad, and was afterwards sent by them to the Landgravine of Hesse: he acquitted himself with honour of all the commissions that were given him. The Duke d'Anguien spoke of him in the highest terms; and the Landgravine received him in the best manner, in consideration of the services which his father had done to the house of Hesse: he was sent a second time by Marshal Turenne to the Landgravine. The Duke d'Anguien promised to take care of this youth's fortune; and the approbation of a prince, who was the Mars of his time and knew men so well, is the highest elogium that could be given of Diederic. He came to an unhappy end when but young and unmarried. Queen Christina having abdicated the Crown in favour of Charles Gustavus, Diederic and Cornelius Grotius took a resolution to wait on that Prince, who had known and highly esteemed their father in France, with an intention to offer him their services, and get employment. Setting out from Holland with this design, they were got between Embden and Bremen, halfway to Hamburg, when a villain, who had served Diederic several years as his valet, resolved to murder both the brothers for the sake of their money: he went in the night-time into Diederic's chamber, and shot his master dead while asleep: he was preparing to serve Cornelius Grotius in the same manner, but he was awake: he happened to be employed in composing a Latin epigram. On hearing the shot, he took a pistol which lay on a chair by his bed side, and seeing the murderer advance softly to him (it was moon-light) he fired, and laid him flat on the floor: the people of the inn got up on the noise, and delivered the villain, who was dangerously wounded, into the hands of justice, and he was broke on the wheel.