Statement from Saudi Press Agency --
Prince Turki bin Abdulaziz told Saudi Press Agency that the alleged letter to him circulated by some media and internet sites was nonexistent and fabricated by enemy parties wishing to spread confusion and excitement.
The statement comes context-free so one is left to speculate why it was necessary, but the Google leads to this story --
Saudi Prince Turki bin Abdul Aziz Al Saud has warned the country's royal family to step down and flee before a military coup or a popular uprising overthrows the kingdom.
The letter is unclear about whether the supposed uprising will be for more or less Islamic strictures than are currently the case, but the main issue with the letter appears to be its dodgy sourcing to an Egyptian news agency and then its propagation by a semi-official Iranian news outlet.
Too many suspects on this one.