“Grey’s Anatomy” might have celebrated its 250th episode on Thursday night but the Season 12 installment was anything but joyous. In fact, a majority of the episode, titled “Look Who’s Coming To Dinner,” was filled with tears, screaming and taking swigs out of a tequila bottle. So what was the cause behind all the stomach-turning chaos?

Well, during episode 5, of “Grey’s Anatomy,” Meredith (Ellen Pompeo) revealed that Callie’s (Sara Ramirez) new girlfriend Penny (Samantha Sloyan), who made her grand debut at the sisters’ dinner party, turned out to be the surgeon who failed to save Derek (Patrick Dempsey) following his fatal, Season 11 car crash.

“The perfect Penny killed my husband,” Meredith blurted out in rage after it was revealed that Penny was headed to Grey Sloan Memorial Hospital to become a resident.

This revelation was catastrophic. Not only did it cause a riff between Amelia (Caterina Scoresone) and Meredith (Amelia was upset that her sister-in-law didn’t tell her who Penny was when Callie’s girlfriend walked through the door) but it also created tension between Mer and Callie. While locked away in her room with Alex (Justin Chambers) and her beverage of choice, Callie attempted to console her long-time friend. But ultimately, Callie had the door slammed in her face by the grieving widow.

After getting shut out by Meredith, Callie opened up to Jackson (Jesse Williams) and revealed that she wasn’t sure how to move forward. She explained that although she cares for Mer, she also cares for Penny -- and she’s not sure she can just stop having feelings for the redheaded doc, nor does she want to.

By the end of the episode, fans saw a light at the end of the tunnel for their favorite Grey Sloan surgeons when Mer (sort of) welcomed Penny into the scrub-sporting family.

“I’ll see you Monday,” she said to Penny after Callie’s girlfriend told Mer she was going to file for a transfer to another hospital. “Don’t be late.”

But, according to Debbie Allen, executive producer of the medical drama, we’re not out of the woods yes! Penny’s episode 6 arrival to Grey Sloan will only result in greater turbulence between Callie and Mer, the EP told Entertainment Weekly.

“It’s great drama. The audience is going to be riveted. I think our viewership is going to triple,” Allen quipped, predicting that the tough predicament Callie is in will peek audiences’ interest. “It’s so amazing what’s going on. Our stories are so based on such real life situations that are not improbable at all. They’re very universal stories. What happens to a family when a wrecking ball comes in? How does everybody react? Who’s sympathetic? Who’s not? Not everyone has the same reaction.”

Nor does it look like everyone will agree with Callie’s chosen of partner. According to Allen, Amelia is “out of her mind” about Callie sleeping with the enemy. “That was her brother, it’s very real for her. She had so many personal life crises. She’s recovered from addiction -- Derek was always the one to help her through all that, and now this happens.”

"Grey's Anatomy" airs Thursday nights at 8 p.m. EDT on ABC.