Diana, the first wife of King Charles, was killed aged 36 in August 1997 when the car carrying her and her lover Dodi al-Fayed crashed in the Pont de L'Alma tunnel in Paris as it sped away from chasing paparazzi photographers on motorbikes.
Swan Song: Diana, My Sister penned by her brother, known as Earl Spencer, is slated to be released next month in Britain and published around the world, telling the story about Diana, from his perspective, according to its publisher Michael Joseph, a division of Penguin Random House.
"With the 30th anniversary of Diana's tragic death on the skyline, I've been inundated yet again with requests for interviews about my sister," Spencer said in a statement.
"This has convinced me to write down my own thoughts and memories, once and for all, rather than having the discomfort of again reading the opinions of others, many of which are based on untruths that have become accepted over time."
Diana became the most photographed woman in the world after marrying Charles in a glittering ceremony in 1981. However, the marriage turned sour and they eventually divorced in 1996.
At her funeral, Spencer famously delivered a eulogy in which he castigated the royal family.
"The aim of this book is to tell the truth about Diana from her brother's perspective, just as I attempted to do when speaking at her funeral. As with my eulogy, I want to speak on Diana's behalf and do so in an openly positive way," Spencer said.
Daniel Bunyard, Publishing Director at Penguin Random House, said it would be a "book of historic importance".
