I have run into a bit of a dilemma in my current story.
The main character is on a journey to save her brother from the enemies. She suddenly finds that he is helping them willingly. Despite this evidence, she refuses to believe that he has betrayed her (her resolution is later shaken).
This scene is followed up with one from the brother's point of view. The scene is meant to reinforce the 'betrayal', along with supplying some information, but unfortunately it does the opposite.
The brother has actually been kept in the dark about what is going on, and therefore does not know that the people he is working with are actively hunting down his sister. During the scene, it is impossible to show that the brother doesn't know what is going on.
I need to make the reader think the brother has betrayed the sister, without showing the reader that the brother doesn't know what's going on. How can I do this?
Note: Before marking this question as too specific, the general question is that if you want the reader to believe the opposite of the truth, when the truth is very apparent, how can you do so?