Empress Farah, the widow of the Shah of Iran, is set to be an unlikely star of the Sundance Film Festival. After repeated requests, she has agreed to speak to me about a new documentary, The Queen and I, in which she is the subject. The film – which has been chosen for the Sundance Festival – was directed by the Iranian-born film-maker Nahid Persson, a former communist who spent much of her early life trying to topple the Shah’s regime. In theory, the two women – the deposed monarch and the revolutionary – should detest one another. In practice, when they came face to face, they discovered they have more in common than either anticipated.