‘Grey’s Anatomy’ season 13 episode 21 spoilers: Maggie confronts Meredith about Nathan

It’s a battle between sisters on the Thursday episode of the ABC medical drama. A confrontation between Meredith and Maggie affects not an operating room, but their personal lives.

Meredith Grey (Ellen Pompeo) and Nathan Riggs (Martin Henderson) are back in Grey-Sloan Memorial Hospital after their ordeal aboard an airplane in the last episode. The two saved a couple of fellow passengers, one from a brain hemorrhage and the other from pulmonary hypertension, after a heavy turbulence hits their plane.

The two decided to work out their differences after the recent in-flight experience, finally giving their relationship a chance. Derek’s widow, however, is still scared on what her sister will say about the romance.

In this week’s episode, Meredith and Nathan appear in a mini-press conference to talk about their heroic acts. Nathan is asked how he compares the experience to his time as a field surgeon in war-torn regions. He says in a teaser for episode 21 that he helped the passengers, but it was Mer who did an exceptional job under a risky situation. Nathan praises Meredith and tells the reporters that the story of heroism should on her. He then touches Mer’s shoulder.

Maggie (Kelly McCreary) sees it all. She is at that conference, where she is supposed to take a video of the event. Then she witnesses the intimate moment. As she observes her sister and Nathan, she will finally realise what is happening between the two. By the looks of the cardiothoracic surgeon, she is ready for a huge face-off.

Maggie has a huge crush on Riggs for a long time, and Meredith knows it. She even promised Maggie that she will not fall in love with Nathan.

McCreary has hinted that her character will eventually accept the Meredith-Riggs romance but will still feel betrayed. "Absolutely. But [on the other hand, Meredith and Maggie have] gone through something so extreme together, and I think the whole Nathan question has been completely irrelevant this whole time. So when it comes up again, I think it becomes about weighing, 'Oh, there's this guy that I liked' against this life-and-death experience that they've shared," the actress told TVLine.

Meanwhile, more challenges are coming up in the Mer-Riggs romance. EP/director/star Debbie Allen teased that the season finale of the series has two huge storylines, one of which involves the new couple.

Apparently, Meredith has some news for her new beau, which will bring their relationship to a turning point. "You should be worried. There's cause for worry. There's an amazing cliffhanger that will have everybody thinking, 'Wow, where is this going?!'" she told Entertainment Weekly.

"Grey's Anatomy" season 13 episode 21 airs on Thursdays at 8 p.m. EDT on ABC in the US. The series also airs every Monday night on Network Seven in Australia.