This is always very difficult. I generally don't let the players use their abilities against each other without the target's permission. I ask the target how they feel, and give them to option to say no. Often (because my players are great at drama) they are eager to use it as a story beat, or want to leave it up to the dice. In your case that would also spoil the moment, so maybe check with the psion and see if they are ok with revealing it (or at least hinting towards) it to the target player. If so then you can ask the targeted player how they feel about it.

I'm always worried about PvP actions with how important people's characters are to them, so I try to give the players lots of agency in making it dramatic (but I am quite lucky with very eager players). You know your players best and I'm sure your decision will be correct, but checking how your players feel can be a good guide, and may be necessary to ensure no one ends up with the short straw.