Alexei inherited hemophilia from his mother Alexandra, a condition that could be traced back to her maternal grandmother Queen Victoria. In 2009 genetic analysis determined specifically that he suffered from hemophilia B. He had to be careful not to injure himself because he lacked one of the clotting factors necessary to prevent him from bleeding to death. According to his French tutor, Pierre Gilliard, the nature of his illness was kept a state secret. His hemophilia was so severe that trivial injuries such as a bruise, a nosebleed or a cut were potentially life-threatening.
The question that puzzles me is: why was this such a secret? There was no shortage of male Romanovs for a succession so even if the Tsesarevich died of his illness the future of the dynasty would not be in jeopardy.
Was there a particular reason to keep this secret or was just the usual Russian preoccupation with secrecy?
Quoted from wikipedia.