Board Thread:Questions and Answers/@comment-81.153.191.71-20150330161821/@comment-25842468-20150331105622

The True Cross Order is aware that Mephisto Pheles is a demon, but I don't think they're aware that he is a son of Satan considering he would've been killed by now if they knew. Like in chapter 10 Shura said she had orders from the Vatican to eliminate anything related to Satan, so that would've included Mephisto if they were aware that he is related to Satan.