But Soderbergh only found a clear way into the story when he read about Liberace's involvement with Scott Thorson, who began a five-year relationship with the star in 1977 - despite his being almost 40 years younger than the man known in his personal life as "Lee".

Using Thorson's 1988 book , Soderbergh suddenly had a structure to hang the story from. "It gave me a character, in Scott Thorson, who is the proxy for the audience. He becomes like Alice and we're following him down the rabbit hole," the director says.

With Douglas on board as Liberace, Soderbergh then had to find an actor to play Thorson. Matt Damon remembers the ambush all too well. The actor had flown to southern Spain to do a cameo in Soderbergh's 2008 two-part drama . Arriving at the hotel, "Steven is at the bar waiting for me and he pulls out a book, . And there's a picture of this young blond guy, and next to him there's Liberace, with all of his rings and a fur coat. Steven hands me the book and goes, 'You. Michael Douglas!'"

That said, when Warner Brothers executive Mark Fritz later responded on Twitter that "it is completely untrue that this film was deemed 'too gay' by Hollywood", Soderbergh backtracked. "The point I was trying to make was not that anyone in Hollywood is anti-gay," he told one magazine, pointing out that his remark was strictly about economics: that the studios wouldn't fund a left-field project simply because mainstream audiences wouldn't go.

In the end, Soderbergh and executive producer Jerry Weintraub petitioned HBO, the cable TV channel responsible for such groundbreaking shows as and . You might even call it a win-win situation; unveiled at this year's Cannes Film Festival, in the US it made its bow on the small screen, raking in the highest viewing figures for an original film premiere on HBO in nine years.

was clearly not "too gay" for audiences who were presumably amused by Liberace sporting his outlandish costumes, the gaudy décor in his mansion, or Thorson parading around in skin-tight Speedos. When it comes to the sex, "there's nothing gratuitous about [them]", Soderbergh says, though even he was taken aback by the gusto of his male leads in these scenes. "They weren't shy!" he says, laughing. "They just did a . They grabbed hands and jumped off the cliff and never looked back."

Still, it would be wrong to suggest the actors were so carefree. Soderbergh can remember a lunch thrown by Douglas at his Malibu home the day before the shoot started. "Matt is sitting there, with his baseball cap on, and he's drinking these kale smoothies because he's trying to lose weight to look buff. And he said, 'Look, what are we doing? What am I playing?' I could tell the reality was starting to hit him. I'd never seen him that anxious before," the filmmaker says.

Damon wasn't the only one. For Douglas, Liberace was the first role he took on since recovering from throat cancer. Soderbergh and Damon put the project on hold while the 69-year-old actor convalesced.

"I'm sure it was because they took a look at me and knew I wasn't ready," Douglas says. "I may have thought I was because I was clean but I was still weak and thin. When you're going through the whole chemo-radiation stuff … the world stands still until you get that clean bill of health."

With the film charting Liberace's stormy relationship with Thorson, it also details his increasing paranoia that the newspapers would reveal he was gay (remarkably his fanbase - largely senior citizens - had no idea about his sexuality). The film also shows Liberace's rapid decline after he contracts HIV and develops Aids (he died in 1987, aged 67).

Given his own battle with a life-threatening illness, Douglas admits those scenes were tough to film. "I know it bothered my father [actor Kirk Douglas] a lot," he says. "He saw the picture and he didn't have a lot to say."

Douglas seems full of admiration for Liberace, a man with a similar lust for his work. "I met him once," he recalls. "He was a very great entertainer, a very generous person. When he'd play his piano, you were just captivated by the fact of how he loved what he was doing."

Soderbergh concurs. "Beneath this flamboyant presentation was this incredible technical skill, and I thought that was interesting. In a weird sort of way, it takes a lack of ego to be willing to hide that ability underneath that extravagant presentation."

Yet despite the lavish lifestyle favoured by Liberace, as Soderbergh points out, his time with Thorson - aside from their 39-year age gap - was not so out of the ordinary.

"They deal with the same issues everyone deals with in a long-term relationship, except it's amplified because of the environment, which is so extreme and so crazy. That's part of what I loved about it. They are having the conversations that other couples have, but they're sitting in a hot tub and drinking champagne."

Now that, as they say, is entertainment.

Behind the Candelabra