HBO is working on another prequel to Game of Thrones, which takes place 300 years before the events of the original series, writes The Hollywood Reporter.

It will be a story about the conqueror Aegon, the founder of the Targaryen dynasty. 300 years before the events of the original series, he conquered most of Westeros with the help of dragons.

HBO will work with Mattson Tomlin, a screenwriter who worked on Matt Reeve’s The Batman and is also co-writing the script for the second installment. The Hollywood Reporter reports that the project is described as a “return to the roots” of George R.R. Martin’s fantasy universe.

HBO has not commented on the situation.