Accoding to IMDb, Eoin Macken (aka Knight Gwain) was in two episodes of The Tudors S4. My friend cotton2cotton found a screencap (click to enlarge). Well, it's a small role with a few lines, but the hair... I am glad his hair is long now.
I also watched Eoin's showreels (2009, 2010). Nice body. He has big ears (usually hidden behind the hair) as well. And he sings (but not so well). Anyway, I have to say I am not blown away by his acting skills. But I guess I should not judge just based on these few minutes. I hope the Merlin writers will come up with a good story for Knight Gwain. Then we can see if Mr. Macken is good for the role. At this time, I am enjoying some shirtless Eoin.