The mystery surrounding the relationship between Nathan Riggs (Martin Henderson) and Owen Hunt's (Kevin McKidd) sister is beginning to clear up in the second half of "Grey's Anatomy" season 12.

TV Line reports that contrary to what most of the fans of the ABC series think, the redhead's sibling is not dead, but very much alive, and she will be coming to Seattle Grace soon. Before the winter break, Owen and Nathan's rift has shifted gears, especially when the former's mother arrived. The moment Evelyn (Debra Mooney) saw Nathan, she was very much surprised that he has been working closely with her son. It soon became clear that they share a close bond, though, as she greeted him like family.

Owen told Meredith Grey (Ellen Pompeo) that the bad blood between him and Nathan was due to his sister. Many speculate that the New Zealander was once in a romantic relationship with her, but things did not work out for them. He might have broken her heart, which explains why Owen hates him so much. Some even predicts she died and Owen blames Nathan for her doomed fate. Another wild idea is that Nathan is a transgender and that he is actually Owen's sister.

In an interview at the Television Critics Association winter press tour earlier this month, Henderson shot down the crazy rumors about his character, stating that he doubted the network would give him such a "controversial or topical" storyline. McKidd, on the other hand, hinted that the mystery would be resolved in episode 14 and urged fans to stop assuming that his character's sister was dead.

"It's more ambiguous than that. There's nothing definite about the fate of his sister," he said.

Meanwhile, the new promo for episode 9 shows the identity of Meredith's (Ellen Pompeo) assailant. He is one of her patients and it remains unclear why he suddenly attacked the doctor. In the clip, Meredith can be seen using a mobile tablet, with her back turned toward the patient. The man suddenly grabs her and pushes her around. Meredith is able to fight back until she comes in contact with the medicine cabinet, the glass breaking because of the impact.

"Grey's Anatomy" season 12 will return on Thursday, Feb. 11, at 8 p.m. EST on ABC.