Troy and Sunshine actress Rose Byrne is in negotiations to join the cast of X-Men: First Class according to THR. Byrne will play Moira MacTaggert, a scientist and an authority on genetic mutation. She’ll also be the love interest of James McAvoy, who will play Charles Xavier.
Olivia Williams appeared very briefly as Moira MacTaggert in X-Men: The Last Stand, appearing on a video talking about mutant ethics and sitting next to Beast at the memorial service for Xavier. In First Class we will probably see more of Moira’s work and her relationship with Xavier.
Here are more details on the character from Wikipedia:
Moira MacTaggert was one of the world’s leading authorities on genetic mutation, earning her a Nobel Prize for her work. She was the longest running human associate of the X-Men and was Professor Charles Xavier’s colleague, confidante, and also once his fiancée, having met and fallen in love with him while they were postgraduates at Oxford University.
Moira’s connection to the X-Men began long before the team formed. The silent partner in the founding of Xavier’s School for Gifted Youngsters and co-creator of Cerebro, Moira assisted Xavier in helping the young Jean Grey recover after the traumatic triggering of her mutant abilities.
X-Men: First Class will begin filming shortly for a June 2011 release.