This was reported on the official page of the series "Game of Thrones" on Twitter.
According to CNN, the prequel will unfold 300 years before the Game of Thrones, it will tell the story of the Targaryen’s house.
It is noted that the series of books “The Song of Ice and Fire” by George Martin will be taken as the basis of the series.
At the end of May, Martin said in his blog that “Winds of Winter” - the penultimate part of the saga “Song of Ice and Fire” - will be completed by the summer of 2020.