User blog comment:Morganaforever/Episode Review: The Diamond of the Day Part 1/@comment-5253758-20121222205654/@comment-5253758-20121222212342

You both realy think that he will stay old? Why would he say that he is a sorcerer then if he is in his Emrys form? All the characters know that Dragoon has magic. It will make no sense.

My best guess (and hope) is that he transformed because he had extra powers or something in his old form so that he could end the battle. Maybe he became old so that nobody (like Gwen for example) could recognize him as he performed his spells.

Spoilers:In a recent preview Emrys is casting a powerful spell and Gwen asks Gaius who that man was. Maybe he just stays like that for a little while so that he can become more powerful. Otherwise, it would be stupid to reveal his powers to anyone because they already know it...