Princess Diana's brother, Charles Spencer, has continually kept his late sister's memory alive following her untimely death in August 1997. Now, Earl Spencer has written a new book, which he believes Diana would have liked.

In an Instagram post shared on September 11, Spencer revealed the cover of his new book, Swan Song: Diana, My Sister.

"Always an amazing, and exhilarating, moment for an author to hold the first physical copy of a new book—and even more so for me with 'Swan Song,' the most personal of the ten books I've written over the past three decades," Spencer wrote in the caption.

He continued, "At heart, this is a brother's simple tribute to an extraordinary sister."

Earl Spencer also revealed that he narrates the audiobook version of the forthcoming book.

"A month ago I read 'Swan Song' out, over three days, for a recording so that it could be available on audiobook," he wrote. "When I finished the recording, I thought: 'That is exactly what I wanted and needed to say—and she would, I reckon, have approved of every word."

Swan Song's synopsis reads, "Beautiful. Beloved. Hunted. The extraordinary life and death of Diana, as told by her brother, Charles."

The synopsis continues, "In childhood, Charles and Diana, the youngest Spencers, were inseparable—secretly calling one another Duch and Carlos. As each other's closest confidantes, they roamed the family estate, endured extremely challenging boarding schools, survived terrifying nannies, and helped each other through the agony of their parents' divorce."

The synopsis further notes, "In Swan Song, Charles Spencer provides the most intimate, loving, and honest portrait yet of his sister."

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