It is confusing all right. The first confusion is that your question reads as though your great-great-grandfather married his OWN great-great-great aunt! However, I deduce that what you were trying to say was that your great-great-grandfather married the great-great-great-aunt of someone you know.
This could be a trick question: if your g-g-grandfather married this lady but they had no children together, and you are descended from another (previous or subsequent) wife, you are not related to this person at all.
However, if this lady was your ancestress, she is your own g-g-grandmother and the sister of one of his great-great-grandparents. In which case, you and this person must share a pair of great-great-great-grandparents, which makes you fourth cousins.