'Spencer' star Jack Farthing says Kristen Stewart arrived on set with her accent already fully formed

• Jack Farthing stars as Prince Charles in the highly anticipated Princess Diana biopic "Spencer."
• The actor also has a role in Maggie Gyllenhaal's directorial debut "The Lost Daughter."
• Farthing spoke to Insider about his roles in two of the year's biggest films.

This autumn there are two highly-anticipated movies where brilliant young women leave their husbands in search of a more fulfilling life. The first, Pablo Larraín's pulsating "Spencer," which stars Kristen Stewart as a high tailing Princess Diana, and the second, actor-turned-director Maggie Gyllenhaal's accomplished feature debut "The Lost Daughter." In both, the British actor Jack Farthing plays the sorrowful spouse, a quirk Farthing pointed out when he spoke to Insider following the premiere of both films at the Venice film festival in September.

"It's weird with both of these projects I felt like you're coming into a marriage right at the end, at the hard bit, when it's falling apart and it's horrible because there's no doubt that there was joy there," he told Insider. "They had some promise and excitement and then it kind of faded."

In "Spencer," Farthing stars opposite Kristen Stewart's Diana as Charles, Prince of Wales, and the film is a much trickier and more ambitious take on the royal couple's doomed relationship than audiences might have seen before. The film is set over the course of a winter break at the Queen's Sandringham estate and charts the deterioration of their marriage and Diana's mental health with appearances from royal ghosts and violent dream sequences. Farthing - who is best known for his work on the TV show "Poldark" - told Insider he was attracted to the role because of what he saw as the "terror" in portraying the life of living royal.

"It's obviously a very scary overwhelming idea, taking on someone like that. Trying to find your own truth in a character that everyone knows so well and is so visible and so recorded and so impersonated," he said.

"I remember Pablo talking about how much he wanted me to feel at home in these big rooms and make them my own and make them feel like I'd lived in them and that's that was a weird process of trying to like go into these rooms beforehand and try and to own the air in them. It's just very weird and difficult."

Kristen Stewart's British accent was complete when she arrived on set, Farthing said.

Thanks to a series of pulsating trailers, "Spencer" has created a lot of buzz on social media and specifically around the potential quality of the American Kristen Stewart's British accent. In a review of the film following its premiere at the Venice film festival, Insider said Stewart is a "perfect" Diana and her British accent was "pinpoint."

When asked whether he had to give Stewart any pointers on how to execute a convincing British accent, Farthing said the former "Twilight" star and California native had her accent nailed before she turned up to set.

"I had nothing to give," Farthing told Insider. "She is incredible. She arrived with everything. She arrived just cooking. She's an amazing person to work with, to work opposite, to kind of play with on set. My first day on set was our big scene over that billiard room table and it was intense. It was really intense and scary. We were just on immediately."

Farthing told Insider that Maggie Gyllenhaal is the best "actor's director" he has worked with.

In "The Lost Daughter," which Maggie Gyllenhaal adapted from Italian author Elena Ferrante's best-selling novel of the same, Farthing stars opposite Jessie Buckley, and the failure of their marriage is depicted across a series of time-hopping, high-energy flashback sequences.

The film, which picked up the best screenplay award at Venice and boasts an A-list cast including Olivia Colman, Dakota Johnson, and Peter Sarsgaard marked Gyllenhaal's directorial debut. Farthing, however, praised Gyllenhaal's directorial style describing her as "phenomenal" and told Insider that Gyllenhaal was one of the best directors he has worked with.

"In terms of an actor's director who you feel cherished and supported and sensitively led by, she's the best I've ever worked with. I think she was just extraordinary," he said. "She's got such an intelligence, like a filmmaking intelligence, and broad outlook and so I think it felt kind of natural to her. And it felt just wonderful to be directed by her. She's so delicate and sensitive and smart and nurturing."

In a review of the film in Venice, Insider said "The Lost Daughter" was a "complex and accomplished thriller" and Gyllenhaal was a director of "great skill and wit."

"The Lost Daughter" hits theaters for a limited theatrical run on December 1 before becoming available to stream on Netflix on December 31. "Spencer" is set for a November 5 release.