The Danish Girl, which most critics say is yet another showcase for Eddie Redmayne's remarkable talent, is not the first time the 33-year-old English Oscar winner is playing a woman.
"I went to an all-boys school and played many women when I was a kid. My first professional job was playing Viola opposite Mark Rylance (on stage) in Twelfth Night, so dressing up as a woman wasn't that new to me," says the actor, who attended Eton school in the same year as Prince William before studying art history at Cambridge University.
In The Danish Girl, he stars as Lili Elbe, said to be one of the first to undergo sex-change surgery, back in the 1930s. The character is Einar Magnus Andreas Wegener, a male artist who enjoyed reasonable success during the early years of the 20th century. He married fellow artist Gerda Gottlieb in 1904.
The couple's story was a starting point for David Ebershoff's debut novel of the same name in 2000, which tells how Einar's posing as a female model for his wife revealed his lifelong identification with the opposite gender.
It's rare that you hear your own voice straight away when you read a script. But that's happened twice with me... And what's disconcerting is that in both, I play a screwed-up, incestuous teenager. I don't know what that says about me.
ACTOR EDDIE REDMAYNE on his roles in The Goat, which won much acclaim, and Savage Grace
For Redmayne, who won last year's Best Actor Oscar for his turn as brilliant wheelchair-bound scientist Stephen Hawking in The Theory Of Everything (2014), Lili represents another opportunity for a powerful and transformative performance.
He says: "I approached this role by meeting trans women of different generations and hearing their experiences. They were incredibly generous in educating me. Then I read around the history of Lili Elbe's story and tried to place the experiences I'd heard about within the context of the 1920s, when there was no predecessor, no example for Lili to look to. There was almost no vocabulary for her experience."
Redmayne's wife, Ms Hannah Bagshawe, a public relations executive he married in December 2014, had no qualms about him taking on the part.
Redmayne says: "I had been attached to the film for a few years, so my wife read the script quite a few years ago and absolutely loved it. Did she give me any tips? No, not really. We would certainly discuss all the people I met during my research and we would talk about their stories.
"Many of them met Hannah as well. Whenever you play a part, it is quite all-consuming, so it is important for me that Hannah is interested and on board because occasionally, the film is all you can talk about for a while.
"The film has taken 15 years just to get made and it has been a passion project for pretty much everyone involved. The fact that it is making it into cinemas is wonderful for us. We are all just hoping that now, people will go and see it."
The film is directed by Tom Hooper - with whom Redmayne had worked on 2012's Les Miserables - and the film-maker claims that the actor is ideal for the part, given his own "gender fluidity".
"He has the gift of bringing the audience with him emotionally," Hooper says of his star. "It is almost as if he is emotionally translucent. Also, there is something in Eddie that is drawn to the feminine. He played girls' roles at school and he was Viola in Mark Rylance's Twelfth Night.
"He has a body of work playing women's roles, which is unusual. There is a certain gender fluidity that I sensed in him that I found intriguing and it led me to think he might be an interesting person to cast in this role."
The arrival in cinemas of The Danish Girl heralds a change in attitudes towards transgender narratives, says Hooper, 43, who won the Best Director Oscar for The King's Speech (2010) and also directed HBO's John Adams (2008) and the celebrated football film The Damned United (2009).
"There has been an incredible and very welcome change of pace in terms of mainstream audiences' acceptance of transgender narratives. We have had brilliant bits of transgender television like Transparent, which is so well acted, directed and written, and Jeffrey deservedly won the Emmy for it," he says, referring to Jeffrey Tambor, who won Outstanding Lead Actor in a Comedy Series at the Emmys last year.
"We have Orange Is The New Black and Caitlin Jenner has been sharing her story, globally, with incredible bravery.
"So there's a tipping point in the acceptance of trans narratives. I only hope that it encourages more of those stories to be told by transgender writers and filmmakers. I hope this is just the beginning."
That said, The Danish Girl has received some criticism.
Redmayne's casting, for example, was not universally well received, some transgender activists saying that a trans actor should have played the role. American actor Jared Leto suffered a similar backlash for his Oscar-winning performance as a trans woman in Dallas Buyers Club (2013).
In his defence, Redmayne says he has taken his transgender role very seriously and has received the support of many transgender women, including his director on the film Jupiter Ascending (2015), Lana Wachowski, and former Vogue model April Ashley.
"Many of the women I spoke to said they had known since they were four or five that they were a different gender from what they'd been assigned at birth," he says. "Then they would describe how they started to transition.
"Some of the women talked about how there would be a period when they first started going out and would perhaps apply too much make-up or put on clothes that were too feminine. One described it as a period of hyper-feminisation and related it to being like a girl going through adolescence, trying different things before she found out who she was."
All of this research fed into his performance.
"I wanted to try and be true to all these experiences," he says.
"Hence, Lili has a red wig and those early clothes and the make-up is quite strong, but gradually, as she becomes herself, she goes back to her own hair and it is all much more pared down."
Redmayne, too, went through a period of discovery when searching for the character - "trying clothes on and trying different bits of make-up, seeing what felt like her and what didn't feel like her".
"It wasn't that I just had clothes put on me. It was more of an intricate discovery."
Going onto the set for the first time as Lili was an interesting and unsettling experience, he recalls.
"I felt the gaze and scrutiny and judgment and didn't know whether that was my own nervousness, but it was unsettling.
"Many of the trans people that I met described going out when they were beginning to transition and there was that mixture of being watched and looked at and scrutinised, but there was also the great threat of violence, whereas for me it was a highly safe environment. They have to live daily with the threat of discrimination."
In his own way, nonetheless, Redmayne has proved a courageous actor from the outset. He left Cambridge with no formal training as an actor, but excelled in demanding roles. A graduate of Trinity College, he first shot to prominence as a theatre performer, his interpretation of a befuddled teenager in Edward Albee's The Goat winning much acclaim.
"It's rare that you hear your own voice straight away when you read a script. But that's happened twice with me very early in my career, first with The Goat and then with the film I made with Julianne Moore, Savage Grace," he says, referring to the 2007 film based on a real-life murder case that took place in London in 1972.
"And what's disconcerting is that in both, I play a screwed-up, incestuous teenager. I don't know what that says about me. In Savage Grace, I sleep with my mother. In The Goat, I snog my father; I had to stick my tongue down Jonathan Pryce's throat, which wasn't particularly pleasant for him.
"Well, it wasn't ideal for me," Redmayne adds with a smile. "But we suffer for our art."
His role in The Goat won him the Outstanding Newcomer nods at the London Evening Standard Theatre Awards in 2004 and at the Critics' Circle Theatre Awards the following year. It also introduced him to Ewan McGregor's American agent Josh Lieberman and to the casting agent responsible for Robert De Niro's CIA drama The Good Shepherd (2006).
Redmayne went on to show his range in diverse movies, including The Other Boleyn Girl (2008), My Week With Marilyn (2011) and Les Miserables, before his career went stratospheric with The Theory Of Everything.
After winning the Oscar, along with a Bafta and a Golden Globe last year for the same role, he was named an Officer of the Order of the British Empire in the Queen's birthday honours list.
"That was surreal and flattering," says Redmayne, who is now filming the lead role of Newt Scamander in Fantastic Beasts And Where To Find Them, the first original screenplay from Harry Potter writer J.K. Rowling.
"It has been an absolute frenzy and all rather extraordinary," he says of his meteoric rise and last year's Oscar hullabaloo.
"I had been working hard making The Danish Girl during the Oscars last year. I finished on a Friday, went to LA for the ceremony and then came back first thing on Monday morning and went straight to the set.
"It is odd. It is a peripatetic lifestyle. So I haven't really had the space to take it all in, if I am totally honest. But once the film I'm working on now is finished, then my wife and I will take a holiday and then maybe I'll have time to think about it all."