Originally Posted by The coin
Panthers are considered "peaceful"
Where have you seen Panther Groupers classified as Peaceful? Groupers are aggressive and territorial. The best bet if you are going to keep it is the idea given to take it out, rearrange the rock, let the others establish their territory for a day or two and reintroduce it. I still think it will end up choosing a new spot and will likely cause the same issues.
As I am sure you know with all of your experience with them, they grow fast and add a tremendous amount to your bioload.
Good luck and keep us updated.