The much vaunted Game Of Thrones prequel reportedly has the working title Bloodmoon, with principal photography already well underway.

It's understood that filming began in Belfast two weeks ago for the new series, which will follow the story of early Westeros inhabitants the Children Of The Forest, according to The Sun.

Naomi Watts was confirmed as the leading role in the series, set five thousand years before the original HBO show.

'Must-watch TV': Game Of Thrones prequel 'has a working title Bloodmoon as stars started shooting the new series' ahead of hotly-anticipated season eight finale

A source told the newspaper: 'Thrones fans will be delighted to hear things have started with the prequel. Those working on the set in Belfast are referring to the series as Bloodmoon.

'Producers have put together a stellar cast and it will be must-watch telly for anyone who loves Game Of Thrones.'

MailOnline has reached out to HBO representatives for further comment.

Big reveal: Stars were said to have started filming, in Belfast two weeks ago for the new series which will follow the story of the Children Of The Forest, according to The Sun

A stellar cast! Naomi Watts (pictured) was confirmed as the leading role in the series set five thousand years before the original HBO show

Naomi will play a 'charismatic socialite hiding a dark secret' but the details of her character have been kept under wraps, according to Variety.

The publication claims the Game Of Thrones' prequel will unveil the 'horrifying secrets of Westeros's history to the true origin of the White Walkers.'

According to the original books written by author George RR Martin The Children Of The Forest are an otherworldly non-human race who were the original inhabitants of Westeros.

Storytelling: Children Of The Forest are an otherworldly non-human race who were the original inhabitants of Westeros

The mysterious beings were living in Westeros when the First Men migrated to the continent 12,000 years before Robert's Rebellion.

Martin has made it clear that none of the current characters or actors will be involved in the prequels because they are set a long time ago.

Jane Goldman's series is one of five prequels to Game Of Thrones which are underway with HBO but Martin set the record straight that the new series are not spin-offs from the original show.

Game Of Thrones concludes on May 19.