The book will recount their childhood, family life, and her transformation into one of the world’s most famous women, while Harry, 41, is planning a Diana documentary to coincide with the 30th anniversary of her death next year, according to sources.
A publishing source said: “There is enormous anticipation around Charles’ book, but the timing is also significant.
“Harry is planning to revisit Diana’s extraordinary life for the 30th anniversary of her death next year, and Charles knows that will create enormous global interest. He has decided this is the moment to put his memories down in his own words and, in effect, get his account of Diana’s life out there before Harry tells the story from a son’s perspective. Effectively, he is beating Harry to the punch on this.”
Spencer has said he decided to write after being inundated with interview requests as the anniversary approached.
He announced: “With the 30th anniversary of Diana’s tragic death on the skyline (next year), I’ve been inundated yet again with requests for interviews about my sister. 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.”
Spencer added his Swan Song book aims to “tell the truth about Diana from her brother’s perspective, just as I attempted to do when speaking at her funeral.”
He noted: “As with my eulogy, I want to speak on Diana’s behalf and do so in an openly positive way.”
Another source said Spencer and Harry’s projects would offer markedly different accounts of Diana.
“Harry knew Diana as his mother, while Charles knew her long before the palaces, photographers and worldwide fame,” the insider explained. “Charles can describe the girl he grew up beside and the family experiences that shaped her. “With Harry preparing to commemorate Diana through his own documentary, Charles’ book means his version will reach the public first.”
At Diana’s 1997 funeral, Spencer made an emotional pledge concerning her sons, Prince William, now 44, and Harry.
He famously delivered a passionate speech at Diana’s funeral in which he referred to his sister’s “blood family” and promised to look after her sons William and Harry.
Spencer declared as the farewell was watched by billions of royal fans worldwide on TV: “I pledge that we, your blood family, will do all we can to continue the imaginative way in which you were steering these two exceptional young men so that their souls are not simply immersed by duty and tradition but can sing openly as you planned.”
Diana was buried on an island on Spencer Estate, Althorp, in Northamptonshire.
Spencer added about his upcoming book: “I hope this book will be of interest to the many who still cherish the memory of Diana when she was alive, and I would be delighted if those too young to remember her in her heyday feel – after reading this – that they ‘get’ who she really was.
“A one-off dynamic character, full of love, charisma and self-doubt, who gave life a h— of a go, and left the world a better place, despite exiting the stage while still so young.”
Daniel Bunyard, publishing director at Penguin Random House UK, said: “Charles Spencer is both a loving brother and an acclaimed memoirist as well as a celebrated historian, and all these facets are brought together in Swan Song. “While these pages contain many revelations that will draw considerable attention, readers will find, for the first time, but also for all time, a fitting tribute to the beloved woman who was Princess Diana.”