Massive fortress appears on coast as Game of Thrones prequel filming begins

Game of Thrones fans have received the first clues that filming of a prequel to the hit show is finally underway.

A huge set has started being built on the UK coast which has led many to believe that House of the Dragon, the long-awaited spin-off to the acclaimed HBO series, has begun production - three years after Game of Thrones ended.

The construction of what seems to be a stone fortress has appeared at St Michael's Mount in Cornwall, with film crew and production trucks having also been spotted in the Newquay area.

With filming due to take place on the Cornish shore, the show is set to air in 2022 (Greg Martin / Cornwall Live)

Rhys Ifans, who will play Otto Hightower, has a read through of the script (@HouseofDragon/Twitter)

On part of the building can be seen the etched shape of a seahorse which some GoT fans have compared to the insignia of one of the families in the fantasy drama.

Set 300 years before the events of its predecessor, House of the Dragon is set to star Rhys Ifans, former Doctor Who Matt Smith and Paddy Considine.

It will tell the story of the Targaryen family, one of the descendants of which - Daenerys Targaryen, played by Emilia Clarke - was a major character in the main series.

The sea horse crest is thought to be connected with the Velaryon family, who were said to be silver haired, with purple eyes and pale skins (Greg Martin / Cornwall Live)

Daenerys Targaryen, played by Emilia Clarke, in Game of Thrones (HBO)

While an official air date for the Game of Thrones prequel hasn't been announced yet, the Twitter page for House of the Dragon has said it will be released sometime next year.

The announcement continued: "Coming soon to @HBOMax in 2022."