The prisoner’s dilemma

The release of two out of three prisoners has been announced but their identity is kept secret. One of the prisoner considers asking a friendly guard to tell him who is the prisoner other than himself that will be released, but hesitates based on the following rationale: at the prisoner’s present state of knowledge, the probability of being released is , but after he knows the answer, the probability of being released will become , since there will be two prisoners (including himself) whose fate is unknown and exactly one of the two will be released. What is wrong with this line of reasoning?