Pandad IV's cat was a Gallifreyan cat and the pet and advisor of Lord President Pandad IV, in accordance with a tradition set by Rassilon's adoption of Tussan's cat in the early days of his Presidency. (PROSE: The Legacy of Gallifrey)
The President's cat was eaten by mutant, gigantic mice accidentally created by an experiment by the First Rani, (TV: The Mark of the Rani) who had been trying to create a formula that would induce rapid growth from fetal to adult stage in biological lifeforms. The grief-stricken Pandad IV, who also lost his High Chancellor to the mice and was forced to regenerate by the ordeal, never got another cat, and neither did any of his successors until Flavia. (PROSE: The Legacy of Gallifrey)