The authors consciously abstain from using the term “schizophrenia” in the title and choose “melancholy,” a condition equated to depression by Albert Frederick’s contemporaries. The goal of the article is to answer the following questions: 1/ What was the illness of Duke Albert Frederick? 2/ What were the reasons for it? 3/ How was his illness diagnosed by his doctors and what treatments they prescribed? The working hypothesis converges with the findings of medical historians to date, stating that Albert Frederick was schizophrenic.