
After marrying Prince William on April 29, 2011, Kate Middleton appeared to develop a strong relationship with her husband's grandmother, Queen Elizabeth II. However, several royal experts have suggested that the late Queen shared some concerns about Princess Kate with friends, and allegedly went so far as to say she had a "Kate problem."
Royal expert Katie Nicholl discussed Queen Elizabeth II's viewpoint in the book William and Harry: Behind the Palace Walls. "If Kate was not with William at Balmoral then the couple were skiing or holidaying on Mustique," Nicholl explained (via the Daily Mail). "Kate was there so often the press dubbed her Queen of Mustique, a title that had previously belonged to Princess Margaret."