An AI model is designed to classify customer feedback into one of three mutually exclusive categories: 'Positive', 'Neutral', or 'Negative'. For a particular piece of feedback, the model outputs the following probabilities:

• P(Positive) = 0.65
• P(Neutral) = 0.25

Due to a software glitch, the probability for the 'Negative' category is missing. Based on the fundamental properties that govern the probabilities of all possible outcomes for a single event, what must be the probability for the 'Negative' category? Explain your reasoning.