Did King Negus convert to Islam?

Did the Christian King Negus convert to Islam? I know that he protected the Muslim who sought refuge in his kingdom, but did he actually convert to Islam. I remember a story in which Negus, at least I think it was Negus, was being asked by his people if he still shared their faith. He wrote out a note and put it over my heart and said something like I believe what is here, putting his hand over his heart and the note, and they were appeased. Does that mean he converted?