The BBC missed out on a massive cash cow when it turned down the chance to back Game Of Thrones from the start.

HBO chief executive Richard Plepler has revealed the British broadcaster was going to co-fund the fantasy drama but pulled out.

For its most recent season GoT pulled in about 20 million viewers for HBO on each episode. But Plepler says back in 2011, even he wasn't completely convinced the show was worth a gamble.

"I was very nervous after I read the pilot script of Thrones because I was concerned that it was a little bit off-brand - we had never done sci-fi in any form - I was worried ... it was very expensive."

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The fact the BBC had pulled out added to his caution.

"The BBC had dropped out. They were going to co-finance the project so it meant that the whole cost burden was on us."

It was one of Game Of Thrones' canny producers, Carolyn Strauss, who managed to convince Plepler to meet with the show's co-creator, David Benioff.

Benioff convinced him the premise of the show was universal, even though it may have seemed "off-brand".

Benioff said it should appeal to Plepler's "political junkie" side as it was basically a story of power and said regardless of where the show was set, he would forget where he was after 15 minutes.

Benioff's passion sealed the deal.

"He looked at me," Plepler said in a recent video interview "and he said, 'I have wrestled with this for the last two years. I understand it, I feel it, I breathe it. There are very few things in my life that I would devote the next 8-10 years to and this is one of them.'"

Benioff promised Plepler he wouldn't let him down. He has certainly made good. Game Of Thrones has become the most popular, and most talked about, show for HBO.

A behind-the-scenes video has caused a stir in the lead-up to the premiere of season six. The video, meant as a tribute to the production crew and camera operators, has been scrutinised by fans for clues - just another sign of the intense interest in the show.

Fans were pleased to see many favourite characters featured, including Tyrion Lannister, Daario Naharis, Daenerys and Jaime Lannister. There was also a possible childhood flashback scene with a young Ned and Brandon Stark. Daenerys' long-term admirer Jorah Mormont is also shown. The series returns in April.

- AAP