"By the Grace of God" means by Divine Right, basically God chose me and my bloodline to govern and rule.

But there is one variation I remember off the top of my head. Eleanor of Aquitaine, wife of Henry II of England and mother of Richard the Lionheart and John lackland/softsword. Wrote an angry letter to Leopold, Duke of Austria after Leopold captured King Richard and held him for ransom for an insult Richard made during the crusade. The letter was demanding Richard's release and signed

"Eleanor, By the Wrath of God Queen of England"