Sour Mix: In a large bowl, whisk the egg whites until frothy. Stir in the sugar and mix until incorporated. Add the water, lemon juice, lime juice, and orange juice. Mix well. Store in the refrigerator until needed.
In a mixing glass, add ice and all ingredients except the Grand Marnier®. Shake to mix and pour into double rocks glass. Top with Grand Marnier® and add lime for garnish.