User blog comment:EmrysOfAlbion/Notes about Series 5 trailer/@comment-4916403-20120722032204

At the end when Merlin say's he'll protect Arthur or die at his side. Maybe he's about to fight Mordred, Morgana, Aithusa or battling with the Saxons and claims he'll protect his knights, he may go out and fight and come close to near death and Merlin could reveal his magic there in order to protect Arthur.

This is just another opinion, what do you think?