Princess Diana's Brother Charles Thinks His Late 'Extraordinary' Sister Would 'Approve of Every Word' in His New Book About Her

Princess Diana's younger brother, Charles Spencer, believes his late sister would approve of the deeply personal story he's finally ready to tell.

On Friday, September 11, the 62-year-old shared an emotional Instagram post while holding the first physical copy of his forthcoming memoir, Swan Song: Diana, My Sister, which will be released on September 22. Spencer called the project the "most personal" of the 10 books he's written over the past three decades.

Spencer marked the milestone by sharing a photo of himself holding a finished copy of Swan Song.

"Always an amazing, and exhilarating, moment for an author to hold the first physical copy of a new book," he wrote, adding that the experience felt particularly significant given how personal the subject matter is.

The memoir marks the first time Spencer has spoken at length about Diana in a book, nearly three decades after her death at age 36 on August 31, 1997.

Despite the intense public interest that has surrounded Diana for decades, Spencer described the motivation behind Swan Song in much simpler terms.

"At heart, this is a brother's simple tribute to an extraordinary sister," he wrote on Instagram.

Spencer and Diana were the youngest of the Spencer children and especially close growing up. In the memoir, he recalls the siblings exploring their family's estate together, navigating difficult boarding-school experiences and supporting one another through their parents' divorce.

Spencer also revealed he recently spent three days recording the audiobook version of Swan Song.

"That is exactly what I wanted and needed to say," he recalled thinking after finishing the recording, adding that Diana "would, I reckon, have approved of every word."

Spencer previously explained that approaching the 30th anniversary of Diana's death motivated him to put his own memories on paper.

After receiving repeated interview requests about his sister, he decided he wanted to tell Diana's story himself rather than continue reading accounts he believes contain "untruths that have become accepted over time."

"The aim of this book is to tell the truth about Diana from her brother's perspective," Spencer explained, comparing his intention to the deeply personal eulogy he delivered at her 1997 funeral.

Swan Song will span Diana's life from her childhood alongside Spencer through her marriage to then-Prince Charles, her transformation into one of the world's most recognizable women and the breakdown of her royal marriage.

The 384-page memoir will also explore Diana's relationship with sons Prince William and Prince Harry, her experiences with the press and the final days leading up to her death in Paris.

Spencer hopes the book will not only resonate with people who remember his sister but also introduce a younger generation to the woman he knew behind the global icon.

He previously described Diana as a "one-off, dynamic character, full of love, charisma and self-doubt," who left the world a better place despite her life being cut short.