User blog comment:Dryuuu/Your reaction to the finale?/@comment-77.6.53.130-20111225070541

"The producers said in an interview an evil character from a previous series would be returning at the end."

I thought that as well, but if you read their comment carefully, it's not what they said. They were answering a question about the end of series 4 and what is about to happen in series 5: They said there would be a twist at the end of series 4, and then - in the NEXT sentence! - they told us about an evil character, who will come back and has a big story arc in series 5. These two things don't necessarily have to refer to the same character/development. So, IMO, the twist was Aithusa helping Morgana, and the evil character, who will return, could indeed be Mordred (whether he's portrayed by Asa Butterfield or another actor).