I'm max ally to Knights of Truth (since I like to kill those darn corrupt guards and give their helmets to needy paladins) so he tells me more than that: "You've managed to show your devotion to the Marr twins which has endeared you to the Temple of Marr and Knights of Truth. As a result, they have authorized me to reward you with a special gift. Take this trinket as a gift and token of your gratitude."
I recieved nothing from him, although it may be an invisible flag. Oh, I should also mention I worship Mithaniel Marr.