User blog comment:Adelina Le Morte March/Why are so many people taking Kara and Mordred's side?/@comment-1208713-20121221174754/@comment-5674726-20121222122829

''Not quite. He told Morgana about Merlin in order to give Morgana the ultimate advantage, thus sealing Merlin's and Camelot's fate.''

In fairness to Mordred, it'd be pretty stupid of him to switch sides yet leave his new ally in ignorance about one of Camelot's chief strengths, and unable to strategise effectively. I'm glad that he wasted no time in sharing the information he had with Morgana.