For centuries, hemophilia was a dangerous genetic disorder with no treatment. Children with hemophilia often didn't make it to adulthood, since a bump or fall could cause massive internal bleeding. But why was hemophilia known as the royal disease? In the 19th century, royal intermarriage meant Europe's royal families shared a small gene pool. And Queen Victoria, the product of generations of cousin marriages, carried a rare genetic mutation that caused hemophilia. She passed it on to three of her children who went on to marry other royal families and spread the disorder.