“I was so gripped by that turn of events,” Michelle Dockery told RadioTimes.com. “I think they did a really good job of not revealing too much as the series went on.”

Holly Berry was Sophie’s studious first year tutorial partner at Oxford University. Following a party towards the end of term, she ran into James on campus, with the pair exchanging a few words, before kissing.

“I should go,” said Holly, visibly unsteady as she pulled away.

“I don’t think that’s what you want to do at all,” replied James, a big grin splashed all over his face.

“No, really,” she responded, before walking off.

But James kept hold of her hand and they kissed again, the moment tender. But in an instant, he was clawing at her body, before he pushed her up against a wall with significant force. She said, “No,” but he didn’t stop, instead instructing her not to be a “prick tease”.

Following her ordeal, Holly left Oxford and fell off the radar. She attended a different university and later changed her name to Kate.

“Kate was a really interesting character to play because there’s lots of layers to her,” explained Dockery. “And she has lots of boundaries, and her personality is quite unreadable.

“She’s quite detached from people. Even the relationship that she has with Richard, it suits her that he is unavailable. And I think that is a way of protecting herself because she has been hurt very deeply.

“Part of the performance was playing that stoicism and not letting anybody in. And then, of course, as the show goes on, you see she begins to unravel.”

How did Sophie clock Kate’s true identity?

The more Sophie observed Kate, both up close and from afar, the more she sensed that they’d met before – on one occasion the pair crossed paths with one another while travelling to their respective destinations, during which their eyes locked, and Sophie unexpectedly arrived at Kate’s office late one night, where they had a brief conversation.

But above all else, it was Kate’s “left-handed scribbling and colour-coded notes” that had jolted Sophie’s memory.

What secret was James keeping for Prime Minister Tom Southern?

Prior to Holly’s rape, James had been at a Libertine gathering with Tom Southern, his friend who went on to become prime minister. Tom had slipped away to the roof to smoke heroin with another student, but James arrived in the nick of time and swiped it off him, before demanding that they head back to their dorms.

On leaving, Tom thoughtlessly encouraged the student he’d been sat on the roof with to jump, which he did and subsequently died.

James vowed to keep Tom’s secret – “Omertà Libertine” – but when Tom was starting to show signs of withdrawing his public support for James due to Olivia’s claims, he threatened to expose him.

“Playing the pariah at the centre of the story was certainly a tall order,” Rupert Friend told RadioTimes.com. “And not necessarily an attractive proposition. But trying to understand where people get this sense of entitlement from and this sense of never having done anything wrong was an interesting challenge.”

He added: “He’s very much an amalgam of people. We didn’t want to make this a biopic about a particular politician.

“But I was very inspired by the politicians who I saw were charismatic and charming and full of potential, but there was a foible or an inner weakness, darkness or secretiveness that was their undoing. There was something quite Greek about that idea.”

Why did Sophie expose her husband’s crimes?