King Charles III has reportedly kept detailed personal diaries for over five decades, chronicling his experiences within the British monarchy and documenting some of its most sensitive secrets. Now, as the 76-year-old king battles cancer, concerns are mounting within the royal family that these private journals may be released after his passing, insiders say.

According to sources, Charles has written extensively about key moments in royal history, including the 1997 death of his ex-wife, Princess Diana, as reported by Radaronline.com. The diaries allegedly reveal his deep regret over his tumultuous marriage to Diana and his long-standing affair with Camilla Parker Bowles, now Queen Camilla.

"Charles refuses to take outright responsibility for Diana's death, but he knows how unhappy he made her by carrying on with Camilla for years," a royal insider said. "That unhappiness drove her over into the arms of Dodi Fayed - and sealed her fate."

Diana and Fayed died together in a car crash in Paris, and speculation surrounding the circumstances of her death has persisted for decades. The source added that while Charles does not believe he directly caused Diana's demise, he acknowledges that their broken marriage played a role in the tragic events leading up to it.

In addition to Diana's death, Charles has reportedly addressed the persistent rumors surrounding Prince Harry's paternity. Long-standing speculation has suggested that James Hewitt, Diana's former lover, could be Harry's biological father. Hewitt has repeatedly denied this, insisting that his relationship with Diana began after Harry was born.

Harry himself wrote about the paternity rumors in his memoir Spare, claiming that his father, Charles, often made light of the speculation. Despite this, sources claim that Charles remains unsettled by the resemblance between Harry and Hewitt and has documented his suspicions in his journals.

Beyond his personal confessions, Charles has allegedly outlined his vision for the future of the monarchy. His diaries reportedly confirm his firm intention for Prince William, his eldest son and the rightful heir, to take the throne. Furthermore, sources claim Charles has given William his blessing to permanently distance himself from Harry and Meghan Markle.

"There's enough circumstantial evidence for Charles," the insider said. "That's why his diaries say he's more than willing to let William permanently exile Harry-and Meghan."