This Is Why Patrick Dempsey Left Grey's Anatomy

If you're at all a fan of television, you're aware of "Grey's Anatomy," the massive, long-running medical drama from creator Shonda Rhimes. The show put Rhimes on the map as the master showrunner she is, and the long-running series is about to air its 18^th season premiere on September 30.

Viewers loved to follow the romantic saga of doctors Meredith Grey, played by Ellen Pompeo, and Derek Shepherd, otherwise known (of course) as McDreamy, who was brought to idealized, fantastical life by Patrick Dempsey. Rhimes kept their "will they/won't they" energy alive for multiple seasons, even after they married in Season 5.

Fans were shocked, and many outraged, when the show decided to — ancient spoiler — kill off McDreamy in a deadly car crash in the Season 11 finale. Amazingly, the show continued without Dr. Shepherd, though he has since returned in memories and dream sequences.

Now, a new tell-all book from Entertainment Weekly reporter Lynette Rice, available September 21, sheds new light on the behind-the-scenes activities of Seattle Grace's residents. The Hollywood Reporter shares an entire chapter from Rice's oral history, "How to Save a Life: The Inside Story of Grey's Anatomy," where she interviews producers, crew, and actors about Dempsey's work on the show, his behavior on set, and his departure — including shocking revelations on why McDreamy was really killed off.

Patrick Dempsey was the most famous cast member when "Grey's Anatomy" debuted, thanks to the 1987 teen romcom "Can't Buy Me Love." Actors and producers gushed about working with the charming Dempsey — at least early on in the show — according to Lynette Rice's book. But apparently after 11 seasons, it grew much more difficult. Dempsey's behavior took a turn, and he seemed to experience some senioritis, making things difficult for his coworkers.

"There were HR issues," executive producer James D. Parriott told Rice, per The Hollywood Reporter, clarifying that they weren't sexual in nature. "He sort of was terrorizing the set. Some cast members had all sorts of PTSD with him. ... I think he was just done with the show."

Dempsey was exhausted, having appeared in almost 250 episodes since the pilot. "It's 10 months, 15 hours a day," Dempsey recalled. "Doing that for 11 years is challenging." But others, like Pompeo, know that's simply the business. There was contention between the two leads: Pompeo would get angry because "she had twice as many scenes in the episode" as Dempsey did, according to producer Jeannine Renshaw, but Dempsey would complain about having to stay late. "He's like a kid," Renshaw said. "He's the kid in class who wants to go to recess."

The final straw came when creator Shonda Rhimes saw Dempsey's behavior for herself, according to Renshaw. "Shonda had to say to the network, 'If he doesn't go, I go.'" Whoa — even more dramatic than on-screen.