In public Diana was fêted wherever she went, greeted by adoring crowds and fawned over by the media. In private she craved anonymity, and it was Ken Wharfe's brief to protect her and keep her away from prying eyes.

The SAS-trained officer from the Yard's elite Special Operations 14, Royalty and Diplomatic Protection Department, was with the Princess every step of the way. As she dazzled among Washington society or walked the sand of exclusive Caribbean beaches he watched over her. In the foothills of the Himalayas, the heat and dust of India and the heart of Africa, he was always just a heartbeat away.

'Purple Five Two' - the woman, the princess - was Ken's charge. In private when they travelled, they often posed as man and wife under assumed names, 'Mr and Mrs Hargreaves', to throw the determined paparazzi desperate for a photograph off the scent. Whenever she wanted a private holiday it would be to Ken she would turn, who would be despatched in secret to find the idyllic spot.

In the six years that Ken was at Diana's side they travelled hundreds of thousands of miles together, sharing secrets, laughter and tears on a truly extraordinary journey. This is their exclusive story.