EXCLUSIVE: Prince William 'On the Edge' as Royal Family Feud Deepens

Prince William is said to be struggling under mounting pressure as explosive allegations about his late mother, Princess Diana, threaten to deepen divisions within the royal family – with his estranged brother Prince Harry's relationship with their uncle adding to the turmoil.

Royal sources have told RadarOnline.com the Prince of Wales, 44, is increasingly distressed following the publication of Earl Charles Spencer's memoir, Swan Song: Diana, My Sister, which contains damaging claims about King Charles, 77, and his reaction to Diana's death in 1997.

The controversy comes amid the monarch's continuing cancer treatment and Harry's return to Britain with his wife, Meghan Markle, 45, placing further strain on an already fractured family.

A royal insider claimed William has been struggling to contain his anxiety about the monarchy's future and the continuing tensions involving his younger brother.

The source described William as a man approaching his emotional limits, claiming the accumulated pressures of his father's health, Harry's activities and renewed scrutiny of Diana's death had left him overwhelmed.

"William is particularly troubled by what he perceives as a growing alliance between Harry and their uncle," the insider claimed.

"William believes the relationship risks turning longstanding family disagreements into another public confrontation, particularly when the monarchy is already facing considerable scrutiny.

"Spencer's memoir revisits the bitter disagreements surrounding Diana's funeral, including whether her sons should walk behind their mother's coffin, and Harry is said to have encouraged his uncle to write it. It is all pushing William to the edge."

Spencer's book alleges Charles appeared "giddily elated" following Diana's death, and he compared the now-King's demeanor at the time of her passing to that of a "lottery winner."

Spencer also claimed Charles told him: "We'll forget her soon enough."

Buckingham Palace disputed the account, suggesting the pain of bereavement could affect recollections of events.

Spencer rejected that explanation, insisting: "Those are exactly the words (Charles) said. I'm telling the truth."

The controversy is also said to have caused concern for Catherine, Princess of Wales, 44, who is understood to be encouraging her husband to avoid becoming embroiled in another public royal dispute.

Our source claimed, "Catherine believes maintaining composure and concentrating on official responsibilities offers the best way forward.

"She has encouraged William to explore relaxation techniques, including meditation, breathing exercises and yoga, to manage the strain."

Catherine and William nevertheless appeared relaxed during a recent film premiere appearance, where they were photographed laughing with Hollywood actor Tom Cruise, 64.

Behind those public appearances, however, sources say Catherine has assumed an increasingly important role in supporting William emotionally.

Further tensions could emerge from discussions; sources claim Harry is "well into" a documentary examining Diana's life ahead of the 30th anniversary of her death next year.

Harry and Markle are said to have explored the possibility of developing the project, potentially through their existing relationship with Netflix.

William previously joined Harry in discussing their mother's life for the 2017 documentary Diana, Our Mother: Her Life and Legacy.

The renewed strain on William comes as Harry and Markle continue to settle back into Britain with their children, Archie, seven, and Lilibet, five.

Diana's death in August 1997 devastated the royal family and triggered an unprecedented outpouring of public grief and sympathy for her sons William and Harry, who were left traumatized by losing their mother at 15 and 12.