EXCLUSIVE 'Grey's Anatomy' Sneak Peek: Is This Meredith and Derek's Biggest Fight Yet?!

Things are getting intense in the Shepherd/Grey household!

All season, tensions have been running high between Meredith (Ellen Pompeo) and Derek (Patrick Dempsey) on Grey's Anatomy and in this Thursday's all-new episode yet another fight is brewing in the bedroom.

To help prepare all of the MerDer lovers out there, ETonline has your exclusive first look at what could be the couple's biggest fight yet!

WATCH: The 'Grey's Anatomy' Stars Would Be Horrible Doctors in Real Life!

At the beginning of the season, Meredith was floored to discover that she has yet another half-sister roaming the halls of Grey Sloane Memorial. Now that Meredith and Margaret (Kelly McCreary) are on civil terms, Derek is determined to welcome his new sister-in-law into their lives — but Meredith isn't having it.

"Are you kidding me?!" Meredith snaps at her husband in our sneak peek scene. "I have to have dinner with the sister I don’t know and the bio-dad she hates because you gave up your chance to work for Obama? You're going to play that card?!"

Take a look at our exclusive clip above to witness the entire vicious verbal throw-down for yourself and let us know who's side you're on in the comments below!

Grey's Anatomy airs Thursdays at 8 p.m. on ABC.