"Grey's Anatomy" certainly rattled fans' cages when the show's most secure couple seemed to be treading on troubled waters. Did Derek really cheat on Meredith? Seasoned watchers of Shonda Rhimes' hit medical drama are well-aware that Meredith called Derek once, only to find a woman picking up the phone. This obviously sent the surgeon into over-drive,  convinced her husband was cheating on her.

Last week's episode provided few answers into the Mer-Der mystery. But what it did show was Derek landing in the middle of the night at Meredith's apartment explaining that he came because a woman answered his phone and that they are in trouble. The burning question that fans continue to ponder over: did he really cheat? According to the episode's official synopsis by TVGuide and the episode's promotional clip, Derek offers an explanation but Meredith isn't buying it, partly because he's done it before with Addison and partly because she has a skeptical nature.

Moreover, teaser clips of episode 17 "With Or Without You" hint that Derek may or may not be having an affair with his new resident, Renee Collier. Essayed by actress Scottie Thompson, Renee Collier is Derek's resident and she is seen holding Derek's hands and passing flirtatious glances at him.

CaterMatt reports that, while the teaser clip is made to imply that he is having an affair, the truth may be that a part of him wants to but he stops himself at the last minute. This would explain why he landed at her doorstep in the middle of the night.

However, Callie is skeptical of Derek after learning he showed up unannounced. She thinks he has done something wrong if he abruptly showed up and apologizes, because it means he has something to apologize for. Meanwhile, Amelia may be meeting Owen's mother sooner rather than later as she turns up at the hospital as a patient.

Episode 17 of season 11 airs on Thursday, March 26 at 8 p.m. ET on ABC.