Paris Hilton must serve 45 days in jail for violating her probation by driving without a valid license.

Handing down the decision May 4, Los Angeles Superior Court Judge Michael Sauer ruled the 26-year-old celebrity heiress must turn herself in by June 5.

A visibly shocked and tearful Hilton called the decision "cruel and unwarranted." She subsequently fired her spokesman, veteran publicist Elliot Mintz. At the hearing, Hilton unsuccessfully argued Mintz had told her she was permitted to drive for work-related reasons.

Paris Hilton's lawyer, Howard Weitzman, says he will appeal. Last September, Paris Hilton was arrested for drunk driving. Pleading no contest in January - the equivalent of a guilty plea - she received a sentence of three years' probation and had her license revoked.

In February, police again stopped her for driving without headlights. Her Bentley was also impounded when it was discovered she was driving on a suspended license.