According to Princess Diana’s go-to biographer, she would be “very upset” by the rift between her sons, Prince William and Prince Harry.

Princess Diana wanted her sons to be best friends and sources of support for one another as they navigated the rigors of royal life. And now that the two brothers are engaged in a “fierce and bitter” feud, one of her closest confidantes believes there’s “no question” she’d be heartbroken.

According to Andrew Morton, the Princess of Wales always viewed Harry, 36, as his elder brother’s “wingman.” If Diana, who died in a car accident in 1997, were still alive today, she would be “very upset” at how the pair’s once-close relationship has become more strained.

“Diana said to me quite clearly on several occasions that she saw Harry as the wingman for William in what would ultimately be a very solitary, somber job as future king,” he said on ITV’s Loose Women.

“She would have been very upset at the way these two have split apart.”

Morton also predicted that if Diana were still alive today, she would be actively trying to assist her sons mend their relationship.

“Knowing [the brothers’] personalities intimately, as a mother would do, she would be working out, perhaps with Prince Charles by her side, a way to reconcile them,” he added.

Morton, 68, spoke on the chat program ahead of Diana’s 60th birthday, which would have been on July 1.

The Princess of Wales died in a vehicle accident in Paris in August 1997. She was just 36 at the time.

Furthermore, Charles is profoundly troubled by the rift between the brothers, with whom he has had a difficult relationship over the years, particularly during the period following Diana’s untimely death in a Paris car accident in 1997.

A friend told PEOPLE exclusively in this week’s issue that Charles, 72, is “shellshocked by it all. He is very hurt and upset.”

Months of rumors over the pair’s deteriorating ties were first hinted to Prince Harry in 2019 when he stated they were on “different paths.”

Within months, Harry and Meghan Markle, 39, resigned as senior royals, a move called Megxit.

In pursuit of a “private life,” they moved to Canada, then to Los Angeles.

William, 39, and Harry, 36, are planning an elaborate event to unveil a monument in their mother’s honor next Thursday at Kensington Palace, their mother’s former home. Intriguingly, the fighting brothers are said to have “insisted” on making separate addresses.

“The Princes hope that the statue will help all those who visit Kensington Palace to reflect on their mother’s life and her legacy,” according to a statement announcing the statue’s commission.

Despite rumors that both parties are attempting to reconcile, their increasingly tense relationship is still being played out in public.

Harry left his Santa Barbara, California, home on Thursday and traveled to the United Kingdom, where he will quarantine for five days before rejoining his brother. Their father, Prince Charles, who divorced Diana in 1996, will be abroad at his Scottish home for the ceremony and is not expected to meet Harry during the Duke of Sussex’s visit to London.