Princess Diana shared one last amazing secret with Paul Burrell days before her death.

In an astonishing letter she noted how amazing this last secret was. And she underlined its nature by remarking: "What an amazing secret!"

The letter to her loyal butler was written in August 1997 - the month of her death in a Paris car crash.

In her last letter she thanks her loyal butler and friend for saving her sanity through the traumas of her personal life: "Thank you so much. I don't know what I would have done had I not got a true, loyal friend in whom I can entrust my amazing secrets including this last one which really is a whopper.

"It's all right, when I die in a car crash in the Place d'Alma tunnel, you can wind up the palace as much as you like with any of the letters I hereby being of sound mind give to you...

"There will be a republic in the UK within 50 years, I feel sure."

The last letter continually emphasizes how amazing this last secret is in this, the last letter she wrote to her loyal butler before she died.

And in an echo of her description of Burrell as The Rock she signs off: "Thank you Paul for being such a tower of buttling strength. Love from Diana."

The letter makes clear just how excited Princess Diana was by this last amazing secret - although there is no mention of her lover Dodi Fayed.

The princess's deeply personal note to Burrell, who shared her innermost thoughts during the four years he worked for her, will bring further speculation about her death.

It will fuel the claims by conspiracy theorists that Princess Diana's death was arranged by 'unknown forces' who wanted to stop her living the life she wished to lead.

And it will start a guessing game as to what Diana meant when she wrote it.

Burrell - who reveals the letter for the first time in his book A Royal Duty, serialized exclusively in the Dully Mirror last week - and available in all good book shops - admits that Diana's destiny would have been changed for ever by her amazing last secret coming true.

"I know the future we were heading to," he writes, "and it was amazing."

Burrell, accused by some including Princes William and Harry of betraying the princess, does not reveal what this last, amazing, secret actually was, but says that it was truly amazing.