Prince William has spoken about his "dark days of grief" following his mum Princess Diana's tragic death in a car crash in 1997.The dad-of-three, who recently visited the university he fell in love with Kate Middleton, appeared in Edinburgh on Saturday 22 May and admitted he was in Balmoral when he heard of his mother's passing.The 38 year old said: "In short, Scotland is the source of some of my happiest memories. But, also my saddest.