Viewers will be able to witness the legendary Dance of Dragons, the infamous civil war.
George R.R. Martin, the author of the books is on board as the executive producer.
He published Fire and Blood earlier this year, a history of House Targaryen spanning roughly 150 years.
The events in the book will be covered in the prequel and is serving as the basis for the show.
Dance of Dragons was a massive civil war in the Seven Kingdoms between two rival branches of House Targaryen and it took place roughly 200 years before the events in Game of Thrones.
Shireen Baratheon in Game of Thrones season 5 provided a short summary.
She read a book about the civil war and described the following to her father Stannis:
“It’s the story of the fight between Rhaenyra Targaryen and her half-brother Aegon for control over the Seven Kingdoms.”
“Both of them thought they belonged on the Iron Throne. When people started declaring for one of them or the other, their fight divided the kingdoms in two.”
“Brothers fought brothers, dragons fought dragons. By the time it was over, thousands were dead. And it was a disaster for the Targaryens as well. They never truly recovered.”
HBO has announced four prequel series that are in the works and recently added a fifth, according to The Hollywood Reporter.
That drama is written by Jane Goldman and Martin and star actors such as Naomi Watts and Miranda Richardson (Rita Skeeter from the Harry Potterfilms).
It takes place a thousand years before Game of Thrones and chronicles the end of the Age of Heroes, a time when legendary figures such as Bran the Builder and Lann the Clever lived in Westeros.