"The interventions of Leopold III caused Himmler's hostility, which led to Kiewitz being downgrading to the rank of captain. After two months of detention, the SS released him for lack of evidence. Kiewitz, on a suspended sentence, was referred to the SS-Sonderregiment Dirlewanger as an officer for special tasks. Nothing is known about his release from the penal unit before October 1944, i.e., most likely, he served in the SS-Sdr.Rgt. Dirlewanger during the Warsaw Uprising. He conquered the capital of Poland for the second time. Kiewitz was wounded in 1945 and lost his right arm. He was taken prisoner by the Soviets, but was released as an invalid in March 1946."
I don't think this guy, a Nazi who went through further hell simply for sympathizing with Leopold during the war, is inclined to lie about how pleasant Nazi prisoner conditions were, somehow. And if this is what they did simply to someone who treated Leopold humanely and with dignity, why would they be inclined to treat Leopold noticeably better?
"The morning after this brief respite from misery, the journey to Strobl resumed its weary pace, traveling towards Salzburg, amidst bitterly cold weather. The royal family spent hours shivering in a tunnel during another bombardment. It was nearly midnight by the time the convoy finally reached the small village of Strobl, in the heart of the Salzkammergut. A wooden chalet, isolated from the rest of the local population, and surrounded with barbed wire fences, awaited the hostages. As at Hirschstein, they would live at close quarters, under cruel and humiliating conditions. Their diet remained poor, although it was fortunately supplemented by the dandelions growing plentifully in the garden. The prisoners' treatment, moreover, became harsher as the months passed, as their routine walks in the garden, initially allowed three times a week, were eventually forbidden.
As described by Roger Keyes in Échec au Roi, the Vicomte du Parc, governor of Prince Baudouin, when asked years later about the period at Strobl, could find no words to describe the horror of these final months in captivity. As the Allied armies approached Strobl, the prisoners feared that they would be massacred by their gaolers, as a desperate, fanatical act of vengeance. The tragic fate of the Romanovs haunted the Saxe-Coburgs... Indeed, at the beginning of May, shortly before their liberation by American troops under the command of General Alexander Patch, an S.S. officer gave Princess Lilian a box of blue pills, claiming that they were vitamin supplements, and advising her to distribute them to the whole family. Duly suspicious, she did not do so. The pills were later tested by the Americans and found to contain cyanide."
"Nevertheless, after the war, Leopold's leftist political opponents, including Prime Minister Achille van Acker, would accuse him of secretly conniving at his own deportation, in order to increase his popularity by posing as a heroic victim."
People tend not to make up stories of terrible treatment and deprivation for sympathy. They tend not to talk about awful things that happened in the war because they don't want to think about it.