The relationship between Alexander I and his sister Ekaterina is perplexing. From a young age, Alexander was involved in romantic affairs, maintaining ambiguous relationships with several noblewomen. However, his connection with Ekaterina transcended ordinary sibling affection, characterized by frequent correspondence filled with endearing words. Ekaterina was stunningly beautiful, and Alexander's feelings for her were complex and profound. Despite the many beauties surrounding him, he kept a close bond with Ekaterina. When Napoleon proposed to Ekaterina, Alexander vehemently opposed the match and ultimately arranged for her to marry a relatively low-ranking German duke. Nevertheless, this marriage did not alter the intimacy between the siblings. The nature of the emotional entanglement between Alexander I and his sister remains a historical mystery to this day.