Princess Diana's biographer has weighed in on Prince William and Prince Harry's longstanding feud, saying their late mom expected her younger son to be his older brother's "wingman" and not a "hitman." This comes on the heels of the coming of the Duke of Sussex's memoir, "Spare," which fears to contain explosive revelations about the royal family.

Prince William and Prince Harry's relationship is believed to be strained after the latter announced his and his wife Meghan Markle's decision to step down as senior royals in 2020. Though they showed a united front after Queen Elizabeth's passing through a walkabout outside Windsor Castle in September, they seemed to have remained at odds with each other.

Kensington Palace and Buckingham Palace are reportedly waiting for the controversial prince's memoir. It's believed the Firm will not get an advance copy of the book, so it must wait for its release on January 10, 2023.

Hence, different speculations surround its contents, with royal biographer Andrew Morton saying Princess Diana would have wanted Prince Harry to support Prince William rather than attack him. He told TIME magazine that the People's Princess wanted her youngest to be her eldest's biggest supporter, not an attacker.

That said, many are waiting to see how well the royal family perceives the revelations of Prince Harry's memoir. Morton himself shows interest in the book, adding he will be reading it once it becomes available.

He didn't blame Meghan Markle's husband, though, and explained that he has "every right" to tell his experiences as a part of the royal institution. He then cited the memoir of Edward VIII, who abdicated the throne in 1936, stressing that the monarchy had survived many things, so it would surely overcome Prince Harry's "Spare."

The Sussexes have reportedly been feuding with the Cornwalls for a few years. However, the Fab Four made a rare comeback to greet the fans outside Windsor Castle when Queen Elizabeth died in September.

Daily Mail claimed it was Prince William's idea to hold a joint appearance with his wife, Kate Middleton, Prince Harry, and Meghan Markle. He reportedly extended an 11th-hour olive branch to his sibling after receiving a phone call from their father, King Charles III.

He initially wanted to bury the hatchet between them. But with the severity of their feud, a source told People that their outing became "awkward, to say the least." Hence, both had a hard time and only put a "stoic spirit" to get through it for their beloved grandmother.