Queen Victoria's son, Prince Leopold, died from haemophilia, but no member of the royal family before his generation had suffered from the condition. Medically, there are only two possibilities: either one of Victoria's parents had a 1 in 50,000 random mutation, or Victoria was the illegitimate child of a haemophiliac man. However the haemophilia gene arose, it had a profound effect on history. Two of Victoria's daughters were silent carriers who passed the disease to the Spanish and Russian royal families. The disease played a role in the origin of the Spanish Civil War; and the tsarina's concern over her only son's haemophilia led to the entry of Rasputin into the royal household, contributing directly to the Russian Revolution. Finally, if Queen Victoria was illegitimate, who should have inherited the British throne? The answer is astonishing.