Valium - I did a history degree but mostly I just love it
Not my profession but I was thinking just today about that......
The mutated gene is the best theory. It can and does happen. The other possibility is that they'd all been carrying it for a while and nothing had happened to pop up - which is surely unlikely or that Victoria's father wasn't the Duke of Kent after all but some random haemophiliac who just happened to have an affair with the Duchess of Kent at the relevant point
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Regarding Princess Alice - one of her daughters (Duke of Edinburgh's sister) was killed in an air accident. She was married to the Grand Duke of Hesse - the grandson of Queen Victoria's daughter Alice, the nephew of the last Tsarina. She herself was the great-grandaughter of Alice - so sort of cousins. She was flying with her husband, mil and two sons to Britain for her bil's wedding when the plane crashed and all were killed. She was pregnant as well. The only survivor of the family was the baby who had been left at home - and who died a couple of years later. Really apalling tragedy.