The biggest battle in the history of “Game of Thrones” is set to take place in this Sunday’s episode, but there have already been some recent casualties related to the blockbuster HBO show.

At least one of the spinoffs for the series that will end after this season has been nixed, a “Thrones” writer and co-executive producer who was working on the prequel confirmed to The Hollywood Reporter. Bryan Cogman told the outlet that though he was developing one of the successor shows with George R. R. Martin — who wrote the “A Song of Ice and Fire” fantasy novel series that “Game of Thrones” is based on — he’s now “definitely leaving.”

“My prequel show is not happening and will not happen,” Cogman told The Hollywood Reporter. “HBO decided to go a different way … So it is a goodbye. I am done with Westeros. It’s wonderfully bittersweet. I’ll certainly miss it, but I’m excited to go out on my own and try to be in the captain’s chair of my own projects, armed with everything I’ve learned.”

Cogman signed a deal last year to create and develop new TV projects for Amazon Studios. He started out as an assistant to the creators of “Game of Thrones” and worked his way up to a co-producing role, writing many of the episodes.

“I’ve learned more than I could possibly imagine from eight seasons of this thing,” Cogman said. “It’s been wonderful to look back and watch some of the old episodes, and see some of our old friends at the premiere recently, and to know that we’ve done something good. We’ve done good work that people enjoy. That’s all an entertainer can ever hope for.