If something is meant to be a secret from the other characters, the "easiest" option is to not discuss it in front of the other players. Sometimes this is accomplished by passing notes (either paper or electronic) to the GM during game, but more complicated conversations may need to take place outside of normal game time. Either way, it's up to you and the GM to determine a method that works for both of you.
That said, there's a different way to resolve it, but it takes buy-in from all the players. Part of what you're afraid of is meta-gaming, the players taking information learned outside the game (that's the "meta" part) and using it inside the game. Some people can't handle a rigid split between player knowledge and character knowledge, others can. You'll have to evaluate your own group to determine that.
IfSome groups may have an objection based on the concept of spoilers. They may simply not want to know in advance. While there is one type of fun in a shared secret with the players can handlein on it, and play theirthe characters appropriately ignorantnot, than there's no reasonsome groups enjoy the players keeping secrets. This takes a certain amount of faith in each other, willing to keep itaccept that any strange behavior on a secret fromcharacter's part is the character messing with other characters, not the player using his character to mess with the other players. Done properly, the reveal can allow the players (and characters) to look back on that behavior and see how the pieces really fit, explaining the strange behavior.
In any of the possible cases, it's a question of the playersgroup's at all.play style, not any individual player or the GM:
- If the players can handle it, and play their characters appropriately ignorant, than there's no reason to keep it a secret from the players.
- If the players don't want to know, then of course keep it from them.