Flegel was a high noble, and the nephew of Duke Otto von Braunschweig. He was involved in the imprisonment of then-Rear Admiral Wolfgang Mittermeyer in 486 Imperial Calendar, paying an interrogator to torture him and after this was unsuccessful attempting to beat him personally. His pride stung by Mittermeyer accusing him of cowardice in beating a manacled man, he released the admiral's handcuffs to fight him fairly but was easily defeated by Mittermeyer and called for his companions to shoot his opponent. This was foiled by the personal intervention of Admiral Reinhard von Müsel at the request of Rear Admiral Oskar von Reuenthal.