Next to You (It's the Rule) (слэш)

Arthur and Merlin have a special relationship. They always have, even when they were prince and servant. While many question it when first noticing, eventually it becomes an understanding in Camelot—and even among some other countries—that where there is Arthur, there is Merlin. And, where there is Merlin, there is Arthur.

Or
Arthur and Merlin's relationship as witnessed and explained by others.
 
Also, or
Five times someone realizes that Merlin is the Queen, one time Merlin realizes it himself, and one time he owns it.