Princess Diana and Sarah Ferguson were once inseparable, famously dubbing themselves the "Terrible Twins" and the "Wicked Wives of Windsor." But a devastating rift between the royal rebels ended their friendship for good.The claim comes from royal author Andrew Lownie, whose expanded edition of "Entitled" delves deeper into the lives and controversies surrounding the former Duke and Duchess of York.Fox News Digital reached out to Ferguson's spokesperson for comment.A spokesperson for Buckingham Palace previously told Fox News Digital it does not comment on books.FORMER PRINCE ANDREW, SARAH FERGUSON DUBBED ROYAL FAMILY’S ‘BONNIE AND CLYDE’ AS EPSTEIN FALLOUT GROWS: AUTHORAndrew Lownie, author of the new book "Entitled," claimed that Princess Diana and Sarah Ferguson had a falling out over Fergie's 1996 memoir, "My Story." (Tim Graham Photo Library via Getty Images)"The two women, once close, had not spoken for months after Sarah had written about her sister-in-law, against Diana's wishes, in her memoir and made a joke about catching a verruca (wart) from one of Diana's shoes," Lownie wrote."The two were fourth cousins and had known each other since they were teenagers — their mothers had been at school together — and shared the experience of their mothers being denied custody of their children."Princess Diana and Sarah Ferguson play around during a skiing holiday in Klosters, Switzerland, on Feb.
17, 1987.(James Andanson/Sygma/Getty Images)Lownie claimed that the sisters-in-law never reconciled after Sarah's 1996 memoir, "My Story," was published.
Diana died in 1997 at age 36 from injuries sustained in a Paris car crash.WATCH: ROYAL AUTHOR DETAILS FORMER PRINCE ANDREW, SARAH FERGUSON'S UNUSUAL DYNAMICRoyal expert Richard Fitzwilliams told Fox News Digital that Diana suspected Sarah of "selling stories" and was reportedly "angered by mentions of her sons in the book."Diana ignored Ferguson's apologies, Fitzwilliams claimed, adding, "If she had wanted to re...