Grey's Anatomy: Owen's big secret revealed! What's next?

Warning: This story contains major spoilers from the midseason finale of Grey’s Anatomy. Read at your own risk!

How many people at Grey Sloan have secret siblings?!

During the midseason finale of Grey’s Anatomy, viewers finally discovered part of the reason why Owen (Kevin McKidd) so desperately hates new doctor Riggs (Martin Henderson) — though it only left us with more questions.

When Owen’s mother (Debra Mooney) makes a return appearance at the hospital — as teased in last week’s Spoiler Room — after her firefighter boyfriend is injured, she curiously and tearfully embraces Riggs. Meredith (Ellen Pompeo) then discovers that Owen had a sister he never told anyone about. In fact, Owen really isn’t telling anyone much of anything, which pushes Amelia (Caterina Scorsone) into Riggs’ orbit as the recovering addict — shocker! — shares a drink with him in the closing moments of the midseason finale. What’s next? EW hit up Henderson to find out:

ENTERTAINMENT WEEKLY: Owen has a sister and seems to hate Riggs for something he did in regards to her. What can you tease of what’s really going on here?

MARTIN HENDERSON: The honest answer is I don’t know exactly. The way they write, we don’t get the scripts until we shoot them, so as much as I nag them to know all of my backstory, they don’t reveal any of that. We’ve shot a few episodes since the one that airs tonight. It hasn’t focused too much on the details, all we know is there was something in our past — some collective shared event — involving Owen’s sister that was tragic for the both of them. They both have very different perspectives of what the actual circumstances were. We do know that Owen’s deeply resentful and angry that I’m back in his sphere. Given how he feels about whatever the circumstances were, he wants me out of there and he’s willing to poison everyone against me. Really, the details aren’t quite clear yet. It’s hinted at that, at one point, Owen and Riggs actually may have been quite close.

Because he’s familiar with Owen’s mom — and even calls her “ma” — is it safe to assume he had some kind of romantic relationship with Owen’s sister?

That’s what I would assume. That definitely seems to be the assumption, but the details are very sparse at this point. They were clearly somehow connected through family and some relationship with the sister.

What are the best theories you’ve heard so far in regards to what might be going on?

Some people were saying that I killed the sister, or maybe I got the sister pregnant and ran off and left her, ran off with another woman. Some people say I was operating on her and she died. I’ve heard all sorts of theories. It’s all very vague at this point.

Will we see any flashbacks to his time with Owen’s sister at all?

I don’t know. That would be cool. That would be nice. It would be fun to do flashbacks if we were all hanging out together, to see young Owen and Riggs out there in the Middle East saving lives. But I haven’t been told that’s the case or the plan. It’s probably a pretty good guess [and] not outside the realm of possibility.

Since Meredith knows the truth, what does Riggs’ dynamic with her look like moving forward?

It’s bumpy. It’s rocky. Though Owen doesn’t give too many details, we know that his resentment runs really deep. He does not paint Riggs as a sympathetic character at all. Based on her loyalty to Owen, Meredith chooses to side and be loyal to him. There’s not a lot of love lost there, and that frustrates Riggs because he has a different perspective on the events and feels that he’s been unjustly tarred. He’s not the kind of person who’s going to run around proclaiming his version. He’s not interested in the politics of what he does so much as the professional job. That’s what he wants to focus on, but that kind of rumor mill, speculation and picking sides tends to alienate him from some of the characters that choose to buy into it. That’s what starts to really frustrate Riggs as we go forward into more episodes, because it makes it harder for him to do his job.

Riggs doesn’t know that Amelia is an alcoholic, but does that bar scene set off a series of unfortunate events in a lot of ways?

It certainly does for Amelia, given what she’s endeavoring to do with her sobriety. Riggs being completely ignorant of that fact is acting purely in a sociable way with no ill intent. He’s not made aware of her alcoholism. Even now, I don’t think there’s been a scene where that information has been relayed to him. From what I understand, I don’t know whether Amelia bothered to even mention to other people that Riggs bought her the drink. I don’t know if she actually did that or would’ve found any reason to do that, but I know that if Riggs were to find out that she was an alcoholic, he would be deeply regretful and apologetic. Obviously that’s something no one would feel good about. Even if you were acting from total ignorance, you would feel bad about playing a part in somebody’s downfall.

If people like Owen and Meredith found out about what role he played in that, would that compound the tension?

Absolutely, yes. It would just fan the flames of contempt, I’m sure. It would be one more indicator of how much they should hate him.

Will Riggs find any allies at Grey Sloan?

He definitely has an ally with April Kepner (Sarah Drew), given their shared history in the Middle East in trying circumstances. What’s interesting is Riggs never even mentioned the nature of his relationship with Owen at all to her, even though she had shared a lot about her relationship with Jackson (Jesse Williams). He was privy to that. As episodes go on, you see him be a sounding board to her and someone she turns to to talk about what’s going on in the marriage and its possible demise. They clearly have a bond and trust there. That’s definitely an ally he has. Also, I think, with Maggie (Kelly McCreary) as well. There’s a shared professional respect there. He probably feels there’s an ally in that camp. Although, she’s also still hearing the rumors and Owen’s take on what happened, so she’s still going to be coloring her opinion of Riggs until more events come to light. It’s fun. I’m the wolf in the sheep’s den. Is he a good guy or a bad guy?

Will the competitiveness between Maggie and Riggs continue?

I hope so. What I like about him is he’s very apolitical. I don’t think he really cares about winning friends over so much as just doing his job. He knows he’s very good at his job, so there’s a very relaxed, quite Maverick way of going about things given his experience in the Middle East and doing things in a more orthodox way. In that arena, one learns to be a little more improvisational, and I think he prides himself on that and actually enjoys the lack of protocol. That kind of thinking on your feet, improvising, finding creative ways to do something, and diagnosing the problem appeals to his personality. That’s going to jar people, so he’s going to continually butt heads with the traditional way of doing things in the OR. If some people respect it, they will, and other people will find it’s not to their liking. He really knows that he knows what he’s doing. If he’s given the chance to do things in an unorthodox way, he’s got a better chance of being successful. He’s not shy about stating his confidence.

Grey’s Anatomy returns Thursday, Feb. 11 at 8 p.m. ET on ABC.