There’s nothing like a little sibling rivalry to end a season, right? On Thursday, fans will watch Meredith (Ellen Pomepo) and Amelia (Caterina Scorsone) go head-to-head in one of their biggest feuds yet during the anticipated winter finale of “Grey’s Anatomy.” (And that says a lot considering we’ve seen a lot of their arguments in Season 12!)

A sneak-peek video reveals the fight between the two ladies will steam from Owen’s (Kevin McKidd) secret hatred for Grey Sloan memorial’s new, hot doc Nathan Riggs (Martin Henderson).

In episode 7, Owen refused to open up to Amelia, his long-time on-again-off-again flame, about his feelings for the New Zealand doctor.

“This is the way Owen deals with stuff when things are bad. He turns in on himself and shuts down,” McKidd explained during an interview with Entertainment Weekly. “I don’t think it’s because he doesn’t trust [Amelia]. It’s just purely that he’s hurting so much right now that he’s closed ranks on himself.”

Although Owen didn’t confide in Amelia, he did open up to Meredith after she revealed to the disorientated doctor that she promised Cristina (Sandra Oh) she’d be there for him when he got all “dark and twisty.”

Of course, Owen and Meredith’s moment rubs Amelia the wrong way, which is when she looks to her sister-in-law for answers.

“Did you find anything out?” she asks Mer in episode 8’s sneak-peek video. But Meredith is reluctant to give Amelia any inside information. “This does not concern you,” Mer responds, adding that she made a promise to help Owen “keep his head above water.”

This outrages Amelia but even more so when Meredith reveals it was Cristina who she made the promise to.

“What does Cristina have to do with this? Are you in some sort of three-way trust circle with Owen and his ex-girlfriend?” Amelia asks, only to have Meredith interject that Cristina was his “ex-wife.”

“God, Meredith. You are the most loyal person I have ever met … to everyone except for me. You’re loyal to someone who is halfway across the world! Cristina left you. I am here. I’m your sister.”

That’s when Mer lays down the cold, hard truth: “You are not my sister. Cristina is my sister. You are Derek’s [Patrick Dempsey] sister and Derek it gone.”

Fans can watch the drama-stuffed Season 12 winter finale of “Grey’s Anatomy” on Thursday, Nov. 19, at 8 p.m. EST on ABC.