With Derek Shepherd's (Patrick Dempsey) elusive fourth sister finally headed to Grey's Anatomy, we now know who is set to play her.

The Gifted star Amy Acker will take on the role of Kathleen Shepherd in an upcoming episode centered around Amelia. Although she was first mentioned in Season 3, this marks the first time the character will appear on-screen. Not much is known about Kate other than that like her brilliant sisters, she received her doctorate degree and works in psychology. She's also said to be married with children but it's currently unknown whether or not her family will also appear.

Discover your new favorite show: Watch This Now!

In addition to Amelia, who was first introduced in the Grey's spin-off Private Practice, we've also met her other sisters Liz (Neve Campbell) and Nancy (Embeth Davitz).

Details about the Amelia-centric episode remain tightly under wraps but with Kate finally coming out of the woodwork, you can expect it to be a poignant and emotional affair.

Grey's Anatomy airs Thursdays at 8/7c on ABC.

PHOTOS: The TV Lover's Valentine's Day Gift Guide