After Princess Diana's death, King Charles experienced an "unbearable emptiness."

King Charles was devastated upon discovering that his former spouse, Princess Diana, had perished in a vehicle collision.

On Aug. 31, 1997, the Princess of Wales, who was 36 years old, died in a car crash in Paris while being pursued by paparazzi. Dodi Fayed, her companion, and Henri Paul, their chauffeur, also lost their lives in the accident.

According to an eyewitness, when Charles was informed over the phone that Diana had died, he "howled like a wounded animal," as Christopher Andersen, author of "The Day Diana Died," told Planet Chronicle Digital.

Andersen stated that Charles was devastated by Diana's death.

The DailyMail reported that a letter written by the former Prince Charles to his friend, detailing his "unbearable emptiness" four months after Diana's death, was sold at auction for $2,000. This prompted Andersen to make his statements.

"When he was first told over the phone that Diana had died, Charles, according to an eyewitness, ‘howled like a wounded animal.'" — Christopher Andersen, author of "The Day Diana Died."

In her final months, Diana's exes set aside their differences for the sake of their sons, Prince William and Prince Harry.

"Diana and Charles decided to put their differences aside and become close friends in the months leading up to her death, according to Andersen. A close friend of Diana's revealed that she still harbored feelings for Charles, despite his infidelity with Camilla."

"Andersen stated that Charles and Diana exchanged affectionate notes, with Charles writing a heartfelt message on the night before Diana's death that read "My dearest Diana" and ended with "Lots of love, Charles.""

She never received it.

After learning about Diana's fate, Charles was overwhelmed with emotions inside the palace walls.

"Andersen stated that the mother of his two young sons was killed in a horrific car crash, and she was also the most idolized woman in the world. Charles had to fight against his mother, the queen, and the entire monarchy to give Diana the funeral she deserved."

Over 2 billion people worldwide watched the ceremonial funeral of Diana, which was attended by 2,000 people.

As Charles mourned, Camilla Parker Bowles faced death threats.

"She had to go into hiding until things calmed down," said Andersen. "As loving a father as Charles, he took the time-honored stiff upper lip approach. Diana's boys were never given grief counseling of any kind. William and Harry were famously forced to walk behind their mother's coffin through the streets of London teeming with a million weeping spectators – what their uncle Earl Spencer later described as 'a tunnel of grief.'"

"Andersen stated that both William and Harry have not fully accepted their mother's death and are still in the process of grieving."

Despite Diana's burial, Charles would continue to be tormented by the recollections and inheritance of his former spouse.

"Andersen stated that Charles believed he would never marry his longtime mistress, Diana, due to the constant obstacles he faced. Despite Diana's death, it took eight years for Charles to convince Queen Elizabeth II to allow him to marry Camilla. The condition was that Camilla would never be known as queen. In the minds of many, the title that rightfully belonged to Diana was taken away by Camilla, who wrecked Diana's marriage to Charles."

Andersen stated, "Of course, Charles broke that promise and crowned Camilla queen."

Charles became king of England after his mother's death in 2022 at the age of 96. He and Camilla married in 2005 and were officially crowned in May 2023.

""Four months after Diana's death, Charles may have confessed to feelings of 'unbearable emptiness,' but it wasn't long before he began to resent the persistent shadow she cast over everything he did, Andersen claimed. Even after a quarter-century, Charles and Camilla still must endure comparison with the incomparable Princess Diana," Andersen claimed."

The king is currently fighting an unspecified type of cancer, according to Andersen, who stated that his illness has caused the 75-year-old to become more contemplative.

"Andersen stated that he believed that Diana's memories, both positive and negative, would always remain with him, lurking in the background. Diana was a larger-than-life figure who became even more prominent in death. King Charles spent years engaging in a shadowboxing match with the ghost of Diana."

It is likely that Charles has had regrets about his marriage to Diana over the years, as previously stated by Andersen to Planet Chronicle Digital.

The marriage between King Charles and Princess Diana was so explosive that violence seemed inevitable, according to a bodyguard's allegations.

To comprehend the heartbreak of Diana's marriage to Charles, one must go back to the start, Andersen stated. Just as Kate Middleton and countless others adorned their bedroom walls with pictures of William and dreamt of marrying the dashing prince, Diana and her contemporaries envisioned marrying [the former] Prince Charles. At just 19 years old, Diana became engaged to Charles, and despite her clear love for him, it was evident that he was still in love with Camilla.

"Charles famously responded "whatever in love means" during a TV interview following his engagement to Diana, while Diana immediately declared her love for him. Despite moments of tenderness, their marriage was a nightmare for both from the start."

During Diana's second pregnancy, there was a brief period when she and her husband became close. Diana considered it the closest they had ever been or would ever be. However, this closeness ended abruptly after Harry's birth. Charles, who had hoped for a girl, made an insensitive comment about Harry's red hair, causing Diana to shut down emotionally.

"Charles deeply regrets being bullied by his father Prince Philip into marrying Diana, despite the fact that it would have meant the absence of William and Harry. The truth is, Camilla was always Charles' true love, and Diana was aware of it."

The Associated Press contributed to this report.