A long-running rift between Prince William and his uncle, Prince Andrew, reportedly stems from a “rude” comment the disgraced Duke of York made about the Princess of Wales, Kate Middleton.

According to royal biographer Andrew Lownie, author of The Rise and Fall of the Yorks, William has made no effort to hide his disdain for his uncle — and fully supported King Charles III’s decision to strip Andrew of his royal titles and honors over his association with convicted sex offender Jeffrey Epstein.

“He [William] also loathes Sarah [Ferguson], Andrew’s ex-wife, and can’t wait for the day when his father throws them both out,” a source claimed in the book, as cited by Daily Mail. “If Charles doesn’t, I guarantee you the first thing William does when he eventually becomes king is to get them evicted.”

Lownie also wrote that William was particularly angered by Andrew and Ferguson’s attendance at the funeral of Katharine, Duchess of Kent, in September. “William was furious at being ambushed in this way,” the author stated. “He has been at pains to distance himself from his uncle and not be photographed with him.”

The book goes on to note that William feels his father has been too lenient toward Andrew, believing that both the Duke and Sarah Ferguson have “done much to undermine the good work of other members of the Royal Family.”

The specific “rude” remark Andrew allegedly made about Kate Middleton has not been disclosed. Reps for Kensington Palace have not commented on the claims.

The tensions between William and Andrew came to a head when King Charles officially stripped his younger brother of all royal titles last week, amid renewed public scrutiny over Andrew’s ties to Epstein.