User blog comment:Merlaa/Dear Brother/@comment-5674726-20121101212235

I think that referring to Arthur as "dear brother" serves a dual purpose for Morgana.

She can emphasise their connection and make Arthur a little hesitant around her, possibly giving her an emotional advantage when they face off.

She is also reminding herself of one of the reasons for her enmity towards him. They're half-siblings - something Arthur remembers when she has a dagger to his back - but their father refused to acknowledge Morgana as his daughter for Arthur's sake. I think that this resentment is a driving force behind Morgana's desire to be Queen of Camelot, because taking the throne is her way of punishing Uther. He disowned her for Arthur's sake so she wants to rule the kingdom Uther intended Arthur to have.