Victoria star Nell Hudson discusses Skerrett's heartbreaking series three storyline

But just as they reach for this happy future, it slips from their their grasp.

Skerrett buys a pregnancy tonic from an apothecary and drinks the contaminated water, contracting the cholera that will kill her.

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The storyline actually came as a surprise to Nell Hudson, who had expected a very different ending for Skerrett and Francatelli.

Having signed up for three series of Victoria from the start, the actress figured that the happy couple would get married and leave the palace and simply disappear from the story by the end of the third series. This was not to be.

"Before we even began filming series three, I went for a supper with [creator and screenwriter] Daisy Goodwin and she broke it to me very gently that, in fact, she had planned a tragic ending for Skerrett," the actress reveals.

"Which, to be honest, was kind of exciting, because I'd assumed that her ending would be a fairytale tied up in a bow. To have it be something so tragic and dramatic, as an actor that's quite exciting. And it wasn't until I read the episode that I then wept and really processed quite how sad it was."

She's not kidding when she says she wept.

"I think it was a Friday, and I'd just been filming all week, and I got the email which was episode four, which I knew was the episode that I pass away in," Hudson recalls. "So I read it on the train back down to London [from set in Yorkshire]. And I was probably tired from a week of filming, but I just cried the whole way back to London. Probably attracted a few stares."

In the episode, Skerrett's decline is painful to watch, as she quickly deteriorates from a healthy young pregnant woman in the prime of her life into a pale cholera victim with sunken eyes and bloodless lips. Perhaps it's no surprise that Hudson had to spend two hours in the make-up chair every morning.

"After I'd had all that makeup done I sent a selfie to my mum being like, 'Here's my death mask mum!' But she wasn't very happy to see me like that," Hudson laughs. "It was a lot of really grey, blue-y, purple-y make-up – very sexy – and they applied this special thing which is really amazing, which is a gel that they put on your lips to make it look like your lips are crusting."

For four days straight, Hudson lay in the sickroom filming her scenes with distraught husband Charles Francatelli (Ferdinand Kingsley).

"It's probably really helpful for Ferdy in saying goodbye to Skerrett, for those scenes, to have me authentically looking like I might actually be about to die," she says. "We filmed that all in order, so it was almost as if we were living it as it was happening... and we were just exhausted afterwards. Because of having to do those big emotional scenes over and over again, it was very tiring – and we went and had a bottle of champagne after completing it!"

One of the most heart-wrenching scenes comes when Queen Victoria (Jenna Coleman) rushes into Skerrett's sickroom, only to find her dying and delirious. "Victoria – if it's a girl," Skerrett manages before crying out in pain. The Queen looks to Francatelli, and he confirms the pregnancy with a pained nod.

That day, says Hudson, was "really upsetting" to film.

"Jenna was just heartbreaking in that scene with her kind of control, as she would have, as Queen Victoria," she says. "But I think what's so heartbreaking about that scene is that Skerrett doesn't really know what's going on. And it was hard not to react to how upset Queen Victoria was, and stay in the delirious ill person confused state."

Still, Coleman did find the perfect way to commemorate Queen Victoria and Skerrett's on-screen relationship.

"She gave me a lovely gift on finishing," Hudson reveals. "She gave me a beautiful real antique Victorian hair pin, because of course when Skerrett was first employed by the Queen, she was there to do her hair. So it was a little homage to the character and a really beautiful thing."

Hudson is now putting Skerrett behind her and taking a very different direction: a horror movie called Petal. "I'm producing a film at the moment, a very Jordan Peele-style horror with a comedic element running through it," she says. "His films tend to be about the role of race within society, and our film is about the role of gender within society. The baddie in my film is the patriarchy. It's quite conceptual.

"I'm starring as the lead in it and I'm also producing it, and that's really exciting for me to kind of get my hands stuck in to the project on both sides of the camera."

When the fateful Victoria episode finally airs in the UK, she says she will be round at on-screen husband Ferdinand Kingsley's house to watch with the rest of the cast.

"I think it won't really all feel real until the episode has aired in the UK, and then it will feel like it's really over," she says. "I'm sure that I'll cry all over again. But it's a bit terrible when you're crying at your own death, because you feel a bit sort of narcissistic! Am I allowed to be sad about this?"

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Still – tears will inevitably be shed.

"When I cry watching the episode I'm sort of crying for Skerrett because she's been such a wonderful character to play; she's so good and courageous and industrious, and I love her deeply and I'm so fond of her, and I'm sort of crying for her and not for me at all," Hudson says.

"And I can't really bear that she didn't get to have everything she ever wanted in the end. I mean she did, for a moment: I suppose that's what we take away from it. For a moment, she had all her dreams come true."

Victoria continues on Sundays at 9pm on ITV