The 55-year-old actor is perhaps best known for appearing in ABC’s long-running medical drama created by famed writer Shonda Rhimes for the show’s first 11 seasons as Dr. Derek Shepard, also known as "McDreamy."
In her upcoming book, "How to Save a Life: The Inside Story of Grey’s Anatomy," author Lynette Rice opened up about Dempsey’s time on set – and his departure, which shocked fans and industry figures alike.
For the book, Rice conducted over 80 interviews with cast- and crew members of the show, both past and present.
"There were HR issues. It wasn’t sexual in any way," former Executive Producer James D. Parriott revealed in an excerpt published by The Hollywood Reporter.
Parriott produced the first two seasons of the hit show before departing. He returned in season 11 to oversee Dempsey’s exit.
"He was sort of terrorizing the set," the exec recalled. "Some cast members had all sorts of PTSD with him."
It wasn’t always that way, however, as in various other interviews, the "Enchanted" actor was described as "so gracious and lovely," "charismatic" and "personable." Actress Brooke Smith even recounted him standing by her and even defending her when she was fired from the show.
However, by season 11, being the center of the show seemingly had gone to the actor’s head.
"He had this hold on the set where he knew he could stop production and scare people. The network and studio came down and we had sessions with them," Parriott explained. "I think he was just done with the show. He didn’t like the inconvenience of coming in every day and working. He and Shonda were at each other’s throats."
Former executive producer Jeannine Renshaw recalled tension between Dempsey and his co-star Ellen Pompeo, who played his on-screen wife. Pompeo, the producer said, would get tired of Demspey’s complaints about how long he’d been on set.
Renshaw noted, however, that upon being reminded that others had been on set longer, the actor would calm down.
Another longtime crew member admitted that Dempsey had a "schtick" but explained that he was "miserable" and "had no one to talk to" once several "rogue actresses" went to Rimes with complaints about his behavior.
Dempsey also was interviewed for the book and said that the lucrative paydays were a huge draw for him to stay, but that he was frustrated with the demanding schedule that kept him from his family.
Renshaw recalled "the final straw," which was when Rhimes "witnessed [the behavior] herself.
"Shonda had to say to the network, ‘If he doesn’t go, I go,’ she said. Nobody wanted him to leave because he was the show. Him and Ellen. Patrick is a sweetheart. It messes you up, this business."
His exit was complicated, and the writers crafted three possible storylines to accommodate his absence, ultimately choosing to kill his character off.
"It was ultimately decided that just bringing him back was going to be too hard on the other actors," Parriott said. "The studio just said it was going to be more trouble than it was worth and decided to move on."
Reps for ABC and Rhimes declined to comment while reps for Dempsey and Pompeo did not immediately respond to Fox News’ request for comment.