"How to Save a Life: The Inside Story of Grey's Anatomy" by Lynette Rice, which will be published on 21 September (21), includes interviews with producers, former cast members, and even Patrick himself about their time on the hit show, which debuted in 2005.
And some of the tome's revelations suggest the 2015 departure of Dempsey, who played Dr. Derek Shepherd on the show for nearly 11 years, wasn't as amicable as it seemed at the time.
In an excerpt obtained by The Hollywood Reporter, executive producer James D. Parriott says, "There were HR (Human Resources) issues. It wasn't sexual in any way. He sort of was terrorizing the set."
"Some cast members had all sorts of PTSD (post-traumatic stress disorder) with him. He had this hold on the set, where he knew he could stop production and scare people... He didn't like the inconvenience of coming in every day and working. He and Shonda (Rhimes, creator) were at each other's throats."
Another executive producer, Jeannine Renshaw, adds there was also tension between Patrick and his co-stars, including Ellen Pompeo, who played first his onscreen girlfriend and later his wife, Dr. Meredith Grey.
"There were times where Ellen was frustrated with Patrick and she would get angry that he wasn't working as much," she notes in the book. "She was very big on having things be fair. She just didn't like that Patrick would complain that 'I'm here too late' or 'I've been here too long' when she had twice as many scenes in the episode as he did."
"When I brought it up to Patrick, I would say, 'Look around you. These people have been here since six thirty a.m.' He would go, 'Oh, yeah.' He would get it. It's just that actors tend to see things from their own perspective. He's like a kid... He's the kid in class who wants to go to recess."
And though he doesn't address the claims against him directly in the book, Patrick admits the days on set were very long, stating, "It's ten months, fifteen hours a day... Doing that for eleven years is challenging. But you have to be grateful, because you're well compensated, so you can't really complain because you don't really have a right. You don't have control over your schedule. So, you have to just be flexible."
He also admits to struggling with his own fame and the show's huge success, sharing, "It's very heady. It (was) a lot to process."
But Patrick, whose character was killed off on the show, has his defenders too, with one insider claiming that though his behaviour wasn't great, he had nobody to talk to when things got bad between him and his castmates.
"All of these actresses were getting all this power," recalls the longtime crewmember. "All the rogue actresses would go running to Shonda and say, 'Hey, Patrick's doing this. Patrick's late for work. He's a nightmare.' "
"He was just shut out in the cold. His behavior wasn't the greatest, but he had nowhere to go. He was so miserable. He had no one to talk to."
Despite all the past drama, Dempsey returned to the series last season to take part in a dream sequence storyline with Pompeo.