Patrick Dempsey, Ellen Pompeo Patrick Dempsey, Ellen Pompeo

Grey's Anatomy may have shocked fans with another half-sister twist, but we actually should've seen it coming all along!

In the season finale, the new head of cardio Margaret Pierce (Kelly McCreary) was revealed to be the half-sister of Meredith (Ellen Pompeo), whom their mother Ellis Grey (Kate Burton) gave up for adoption. Her father? Dr. Webber (James Pickens Jr)!

Forgot what happened in the Grey's Anatomy finale? Read our recap here

How will Meredith react to this new revelation, especially in the wake of Cristina (Sandra Oh) leaving? sat down with showrunner Shonda Rhimes to discuss the upcoming season, including the state of Meredith and Derek's (Patrick Dempsey) marriage after her sudden decision to stay in Seattle, how Amelia (Caterina Scorsone) will change the dynamic and how Alex (Justin Chambers) becoming a board member will shake up the hospital.

Will there be a time jump when Grey's returns?
Shonda Rhimes:
No. We're not going to time jump.

Introducing Maggie on the show is different from the other half-sisters because it also affects Richard. How will this change the hospital dynamic and how will you handle explaining how Ellis Grey was able to hide this pregnancy?
What's interesting for us is that Maggie has been a piece of story that we have had and known about since Season 4 — well, honestly since the beginning. That was one of the original pieces of story since the beginning with the Richard-Ellis dynamic, but it's been a piece of story since Season 4 when we talked about introducing her. We were going, "When's the right time?!" and we were holding it forever. I kept going, "Not this season, it's not right." After a while, I was like, "We're never going to introduce it. The show is going to end without it." Every time I thought the show was going to end, I was like, "Ah!" Then we hit this moment in time and I remember walking into the writers' room and going, "You guys, it's time." And all the writers knew exactly what I was talking about. It's going to be interesting to see how it plays out. Because we've all known about it for so long, it's always been layered it. It's not a thing where we're going in and backdating. It's literally always been layered into the story line. We can literally go back and pull out moments of the show and I'm excited to do so, and point out where it was talked about. It's not going to be so hard to do.

Do you need to bring back Sarah Paulson to show that?
We've talked about the flashback moments and what to do with those. Sarah Paulson has a job, unfortunately. But, we've flashed back both with Kate Burton and Sarah Paulson at the same age. If you noticed the carousel moments with Richard and then Paulson in the hospital with young Richard, they were the same age, we just used younger actors for some reason. So, it can be done either way.

Grey's Anatomy promotes Caterina Scorsone to series regular

How will Meredith feel about that? And will Webber keep this a secret or spill the beans fairly quickly?
What Webber does with the information is going to be very interesting. When she left, she had said something to Richard. Whether Richard admits his part in it at all is going to be very interesting. It's very earth-shattering information. It undoes everything Meredith thought to be true about her past and her childhood. It's fascinating.

Where does this season find Meredith and Derek because she decided she didn't want to go to D.C.?
That is where we start them out. It is something huge. I'm not going to say it causes a huge fight, but we start them out exactly where we left them in the middle of that dilemma. It may cause a huge fight, but I'm not going to say that.

How much will Cristina's presence be felt this season?
I have a person who is that kind of person and I can't imagine suddenly pretending that they don't exist anymore. We've really talked about layering in that idea that she's still there. One of the things that we've talked about is she's on the other side of the planet — you call somebody there and it's nighttime when it's daytime here. So, there's a lot of missing each other, but we want them to still be there. That separation does breathe. Time slowly makes those moments longer.

Will Owen start to move on and get a new love interest?
I don't know yet. We're feeling that out. That;'s an instinctive thing for me. Does it feel right yet? Does it feel good? Do we feel OK about that? Or does it feel icky? And I don't know yet.

What about Amelia and Owen?
I know, right? Because somehow that feels exciting. I've had that thought and I don't know yet. I'm not interested in pushing that because I don't know yet. I think they have interesting personalities and I think they have interesting pains that one another could possibly solve.

Does Katherine Heigl regret leaving Grey's Anatomy?

How are April and Jackson dealing with the pregnancy?
They're being forced to grow up in a way that's amazing. They did a spontaneous thing and things are starting to get serious. They have his mother to contend with, they have the future to contend with and being Averys to contend with and what all that means for them.

How will Bailey feel about Yang giving her position on the board to Alex?
Bailey is not going to go quietly. Bailey has taken a lot of crap and had a lot of hits, and Bailey is done having a lot of hits. I do feel like she has been very overlooked and underestimated. She may be done with that at this point.

Will Alex feel bad about this or is he ready to step up at the hospital?
I think Alex is looking out for himself and that is not wrong from his point of view.

With Amelia coming in full-time, will you be able to tell more Shepherd family stories and finally introduce the elusive fourth sister?
The fourth sister! I love that we slowly deploy Shepherd sisters and Grey sisters. Obviously we love Tyne Daly [who played their mother]. Having Tyne Daly on the show is always a dream. It's an expensive dream, but it's a dream. If it's possible for us, we'd love to do it. My dream episode is where Derek has to go home and deal with all his sisters at once and his mother. That would be an amazing episode. But that's my budget for the year. Maybe one day,  hopefully.

Grey's Anatomy returns Thursday, Sept. 25 at 8/7c on ABC.

Stay tuned for scoop on Calzona in this week's Mega Buzz!