User blog comment:Emily Windsnap/Behold! The Reveal!/@comment-5788405-20121216055507

guys any of you remember the episode "Death Song of Uther Pendragon". Remember the scene where Arthur is knocked out by Uther and Merlin steps in. I have always felt that Arthur was not knocked out but just pretended to be so, may be to think or trick Uther and Merlin unaware of this steps in to reveal his magic to Uther. I feel that Arthur knows Merlin's secret from that point onwards.

May be Arthur is keeping quiet coz he knows Merlin is wise. Don't forget he always asks Merlin to advice. May be he feels that Merlin has hidden his powers for some reason.