The real title of this music is not known. There are essentially two versions of it. The first is in KQ3 at the end when Alexander returns to Castle Daventry, and its used as an victory/ending theme.
Another version of it occurs in KQ1 on the Apple IIGS replacing Greensleeves as the intro music (trivia, this is the third version of the intro music to appear in KQ1 AGI since the original 1984 version). A shorter version of it is used as the introduction music for Edward when you enter the castle.