While we anxiously await the Grey’s Anatomy’s firefighter spinoff, there’s still plenty of drama over on the original series. (Spoilers ahead for the September 28 and October 5 episodes.)

On the season 14 premiere two weeks ago, McDreamy’s neurosurgeon sister Amelia Shepherd was diagnosed with a brain tumor — something that the actress who plays her, Caterina Scorsone, was actually relieved to discover.

Any Grey’s fan will tell you that Dr. Shepherd’s behavior over the last couple of seasons has been… well, unpredictable. She’s had issues in the past, of course — her drug addiction was a major story line on Private Practice — but recently she’d been especially erratic.

“When I heard about the story line, my initial reaction was, ‘So that’s why!'” Scorsone told E! News. “Because it is definitely apparent that Amelia’s behavior has crossed over from a place of ‘Oh, she’s quirky and she does kind of wild, bold things’ to ‘What is she doing?’ in a kind of disturbing way.”

The actress went on to say that, looking back, something was definitely awry. “She was making decisions that were just erratic and not consistent. They didn’t have any line of consistency. She’d say one thing and then she’d do another, and she’d leave because she was freaked out about one thing and get in a fight. It just seemed like it wasn’t respective of her personality… something was off.”

Scorsone said she usually keeps herself in the dark about upcoming plot twists because she wants to “not know what [Amelia] doesn’t know.” But she confessed to E! that she approached people behind the scenes about this situation. “We kind of had a few conversations about it like, ‘Why is she doing this.’ So, hearing that there was actually a physical, medical reason for some of the erratic behavior actually felt pretty good. It made a lot of my questions disappear.”

Shepherd will undergo surgery on tonight’s episode (Thursday, October 12), but that doesn’t mean that all of her troubles are over. In fact, things might be even worse as Amelia recovers. “It’s not a walk in the park,” Scorsone told E! News. “I think she does not wake up immediately from the surgery, ready to go. When she wakes up, it’s pretty scary. It’s touch-and-go for a minute.”

We’ll be able to see just how scary things get when Grey’s Anatomy airs Thursdays at 8pm on ABC.

Were you relieved to find out that there was a medical explanation for Dr. Amelia Shepherd’s erratic behavior? Let us know @BritandCo!

(Photo via ABC/Mitch Haaseth)