'Grey's Anatomy' Enlists Amy Acker for Key Role

Fifteen seasons in, ABC's Grey's Anatomy is finally introducing one of its frequently mentioned but never seen characters.

The Gifted star Amy Acker has been tapped to play the fourth Shepherd sister in an upcoming episode that focuses almost exclusively on Caterina Scorsone's Amelia Shepherd. An airdate for the episode has yet to be determined.

While Acker's casting is a one-off, it's a big deal within the history of Grey's Anatomy. Of Derek's (former leading man Patrick Dempsey) four sisters, only three had ever appeared on the ABC medical drama in its 300-plus episodes. They are: Scorsone's Amelia (a series regular who launched on Grey's but moved to spinoff Private Practice and returned after the latter wrapped); Embeth Davidtz previously appeared as Nancy; and Neve Campbell had a brief arc as Lizzie. But the late McDreamy's fourth sister, Kathleen, had — until now — never appeared.

Kathleen Shepherd appears as Meredith (Ellen Pompeo) this season has really opened herself up to dating and finding love again. Amelia, meanwhile, is entangled in a complicated love triangle with Owen (Kevin McKidd) and Teddy (Kim Raver).

Acker's credits include Person of Interest, Dollhouse, Alias and Angel. She's repped by APA and Anonymous Content.