David Benioff and DB Weiss are in high spirits. With Game of Thrones a distant memory, its creators are fired up about their latest TV show, 3 Body Problem, and there isn't a dragon in sight.
Game of Thrones ended after 59 Emmys and eight series in 2019. Having shelved a Star Wars trilogy that year, Benioff and Weiss chose to adapt a best-selling Chinese sci-fi novel.
Liu Cixi's The Three-Body Problem, published in 2008, has sold up to nine million copies worldwide, and won a Hugo award.
Without spoiling the plot, it's about advanced aliens invading the Earth. They're fleeing an unstable solar system with three suns orbiting each other - hence the name, Three-Body Problem.
The book has two key characters trying to outsmart the aliens, a scientist and a detective, but the TV show's creators felt that this wasn't enough.
So with Liu's blessing, there are five young, diverse Oxford scientists trying to beat the aliens. Well, technically four, as the fifth, played by Game of Thrones' John Bradley, is a millionaire who used his scientific knowledge to create a multi-million pound snacks empire.
Snacks are always useful in a crisis.
They try desperately to solve problems in a deadly virtual reality game, which coincidentally has three suns, while also trying to save the Earth from alien onslaught.
They're watched by a world-weary Mancunian detective, played by Dr Strange star Benedict Wong, and a senior official, played by Game of Thrones' Liam Cunningham.
Thrones creator Weiss explains they were blown away by the book's complexity, calling it "unlike anything we'd ever read, certainly unlike anything we'd ever contemplated bringing to the screen".
Thrones creator Weiss explains they were blown away by the book's complexity, calling it "unlike anything we'd ever read, certainly unlike anything we'd ever contemplated bringing to the screen".
Other fans of Liu's novel include ex-US president President Barack Obama, who called it "wildly imaginative" - although he ultimately declined a small role in the show.
"He did sign a very funny note, when we tried to get him for a cameo," Benioff told USA Today.
"It was to the effect of, 'In case there ever is a real alien invasion, I think I should probably save myself for that crisis'."
But after so much success in the fantasy genre - why did Benioff and Weiss leave it behind?
They tell BBC News it was simply time to move on.
Despite their huge fanbase, not everyone was delighted with Game Of Thrones' finale; 1.8m fans even signed a 2019 petition demanding the eighth series be remade, with a different script.
But Benioff and Weiss didn't want to return to that world, having spent "10 solid years" making 73 episodes in the Kingdoms of Westeros.
It was "the greatest experience of our lives," says Weiss, but they really wanted "a new set of challenges on every level".
Weiss calls 3 Body Problem "about as far away as you can get from what we'd just done on Thrones".
Ready for a new challenge, they had to be picky.
The issue was that Game of Thrones had set a high bar for their expectations.
"You show up at work every day and are kind of amazed you actually get to do this for a living - and that's the feeling that you're chasing," Weiss says.
"Whenever you choose a job you're spending years of your life on, you don't want to make the wrong choice - it's pretty easy to get bored."
Having finally decided on Liu's book, the duo became a trio, joining forces with Alexander Woo, who created vampire TV series True Blood.
Woo calls the novel "a very exciting challenge to adapt", adding: "There were ideas, images and stories in there, and I almost couldn't conceive of how one author could have come up with this."
He agrees it's crucial to choose the right project, given how all-consuming it inevitably becomes.
"If you don't feel exhilarated by it, it's a slog. It's a really, really dreadful way to whittle away your life unless you love it," he says.
"If you don't feel exhilarated by it, it's a slog. It's a really, really dreadful way to whittle away your life unless you love it," he says.
The three of them have worked on 3 Body Problem for the last four and a half years, with a crew of about 1,000 people.
The book is full of knotty scientific problems, which were not easy to translate into a TV show.
A crash course in physics was needed, and the show's creators say they would have been lost without the help of two scientific experts.
They spoke to Matthew Kinsey, who Weiss says was "on the team that discovered the Higgs Boson particle", and Bobak Ferdowsi, a flight engineer at Nasa's Jet Propulsion Laboratory.
"Bobak has been in many control rooms when they were launching rockets," Weiss explains.
The two scientists "kind of walked us through physics for dummies" and were crucially on hand throughout the series.
The show begins during China's Cultural Revolution in 1966 and goes through to present-day UK, via Badajoz in Spain, New York's United Nations Headquarters and Florida's Cape Canaveral. Plus quite a lot of outer space as well.
Weiss and Benioff were familiar with the UK, having used it as a location for Game of Thrones. Returning was was the perfect excuse to loop up with some former cast "Thrones friends" including actors Bradley, Cunningham and Sir Jonathan Pryce.
Bradley had played the fearful, kind-hearted Samwell Tarly in Thrones, and Benioff says they delighted in creating a completely different character for him.
"Dan [Weiss] and I were in a pub in Belfast, and we saw John talking to an American tourist. He was so funny and sarcastic - it was a side of him we know quite well, from having spent a lot of time with him.
"The real John is nothing like Samwell, so we thought it'd be fun to write a role that was closer to the real him."
The result was snack merchant Jack Rooney, who gets some of the show's best one-liners.
The result was snack merchant Jack Rooney, who gets some of the show's best one-liners.
When they cast Wade, a gruff character who leads the fight against the aliens, they went against the book's depiction of "a 40-year-old American who looks like Hugh Jackman".
Instead they hired Liam Cunningham, who played the knight Ser Davos in Game of Thrones.
"I love Liam, but I don't think anyone could accuse him of looking like Hugh Jackman!" Benioff laughs.
"But he's just so great and, again, it's a very different role."
They also cast Sir Jonathan, who played Thrones' religious fanatic High Sparrow, as billionaire oil tycoon Mike Evans.
Benioff calls him "one of the great living actors" while adding they "basically begged" Dr Strange star Benedict Wong to join the show, as Mancunian detective Da Shi.
The show also has some very strong, fiendishly bright female characters holding the plot together, played by Rosalind Chao, Jess Hong, Zene Tseng, Eiza González and Marlo Kelly.
It's clear Benioff, Weiss and Woo are enjoying the ride - just after I ask them not to tell me what happens in the last episode, Benioff drops a huge plot spoiler into the conversation.
"I just hope people aren't too upset with the world blowing up in episode eight, and they keep watching," he deadpans.
They immediately erupt with laughter - he said it just to see the look on my face.
I can report it turned out to be entirely untrue.
Rebecca Bailey wrote for AFP last year that "Chinese science fiction has exploded into the mainstream" - The Three-Body Problem is already a 30-episode TV series in China.
She added: "The global success of the Three-Body series changed everything, catapulting its epic themes of technological prowess and the fate of humanity into the public consciousness."
The show's creators are hoping to capitalise on this popularity - the novel is the first part of a trilogy, called Remembrance of Earth's Past - and they want to finish the story.
"I hope it's as big as Thrones," says Benioff.
"Our goal really is to get to the third season."
3 Body Problem is released on Netflix on 21 March.
