Shonda Rhimes managed to leave “Grey’s Anatomy” fans with their mouths agape once again with the final scene of the Season 10 finale. The twist? Cristina Yang’s replacement, Margaret Pierce, played by Kelly McCreary, is actually Meredith Grey’s half-sister.

It was Dr. Webber who learned the thrilling fact first when Maggie, the new head of cardio, suggested she had applied to Grey Sloan Memorial Hospital because it was where her mother, Ellis Grey, had worked. Yep, not only is Margaret Meredith’s young sister, but she’s also Dr. Webber’s daughter! How’s that for a daddy-daughter reunion?

How will Meredith react to yet another half-sister falling into her scrubs? Well, Rhimes told all when the medical drama mastermind sat down with TV Guide for an interview.

Rhimes explained that the role of Maggie had been an idea waiting to be carried out since the series premiere in 2005.

“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,” Rhimes explained, adding that she had to wait until the perfect moment to introduce this game-changer.

“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.”

Rhimes divulged that Maggie’s debut will be an interesting situation to watch play out.

Grey's Anatomy season 11 spoilers "Grey's Anatomy" creator, Shonda Rhimes, explained that the character of Maggie will be very interesting to watch play out in Season 11. Photo: ABC/Grey's Anatomy

“Because we've all known about it for so long, it's always been layered in. 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,” she revealed.

So, can fans expect Sarah Paulson (who played the younger version of Ellis) to don her surgical gloves once again in Season 11? Alas, Rhimes explained, the “American Horror Story” star won’t appear to give Maggie’s debut context.

“No. We're not going to time jump,” she said. Rhimes added that the premiere of the eleventh season wouldn’t have any flashbacks.

But who needs time jumps when the drama is in the present? According to Rhimes, the truth of who Maggie really is will be “earth-shattering information.”

“It undoes everything Meredith thought to be true about her past and her childhood. It's fascinating,” she teased. Rhimes also added that Webber will do something “very interesting” with the information given to him.

What do you think Rhimes is hinting at? Will Webber use this information to his advantage? We know he will eventually spill the beans, considering when he does “it undoes” Meredith completely. Sound off in the comments section below with your Season 11 predictions of “Grey’s Anatomy" before the series returns Sept. 25 at 8 p.m. EDT.