: Tension peaks when Callie’s new girlfriend, Penny, is revealed to be one of the doctors who failed to save Derek. Penny eventually joins the hospital as a resident, causing friction with Meredith and Amelia. Relationship Turmoil :
: Martin Henderson joined the cast as Dr. Nathan Riggs, whose arrival triggers a dark history for Owen Hunt involving his missing sister.
: Miranda Bailey successfully campaigns to become the hospital’s first female Chief of Surgery . Greys Anatomy - Season 12
: Alex proposes multiple times, but Jo repeatedly declines because she is secretly still married to an abusive man she fled years prior. Cast Transitions
: This season marked the final regular appearance of Sara Ramirez as Callie Torres. Reception & Ratings : Tension peaks when Callie’s new girlfriend, Penny,
Season 12 of Grey's Anatomy , which premiered on September 24, 2015, is often described as the "season of rebirth". Following the death of Derek Shepherd in Season 11, the show shifted to a noticeably lighter, more "rom-com" tone, reminiscent of its earliest seasons.
'Grey's Anatomy' Season 12 Trailer: "Everything Has Changed" Nathan Riggs, whose arrival triggers a dark history
: The couple's marriage collapses, leading to a divorce. However, they discover April is pregnant shortly before signing the papers.