Kick-Ass star Aaron Taylor-Johnson has revealed how difficult it was for his director wife Sam to deal with his latest film role.
The British actor plays a Texan psychopath in Nocturnal Animals, the second film of fashion designer Tom Ford, and he said his wife breathed a sigh of relief when filming was over.
Arriving on the red carpet at the premiere at the BFI London Film Festival, he said: "It was a very toxic experience, it was pretty unpleasant.
"My wife was very pleased when we left that one."
Aaron, who has two daughters with the 50 Shades Of Grey director, added: "It took a very long process of researching this role, I grew my hair out and Tom wanted me to grow my fingernails out and I was spending a lot of time at night watching and studying psychopaths and serial killers, Ted Bundy, Jeffrey Dahmer, things that made me not sleep at night.
"I had an aura of that around me that wasn't very nice, that I needed to shed and which took a lot of time."
Tom, who also wrote the screenplay and produced the film, said he watched his friend go through a huge transformation as he slipped into the character.
He said: "He stayed in character, he worked on it for quite a long time.
"Aaron is a friend and even in our friendship world, having dinner with his wife, I watched him become another person.
"He inhabited that role while we were filming.
"I think his wife was quite happy when we stopped and he returned to his nice, calm, normal self. She said 'thank you for giving me my husband back'."
Tom's second film follows 2009´s A Single Man, which starred Colin Firth, and the designer said it addresses issues close to his heart.
He said: "The overriding theme is about finding people in your life that you love, that mean something to you and not throwing them away.
"I'm a very loyal person, I've been with the same person for 30 years, that has enriched my life and that is the theme of this film."
Aaron's co-star Amy Adams does not share any scenes with him in the film but said she saw the impact of his role in an unexpected place.
She said: "Our children are in the same school together, they are in the same class, so I got to see him in the mornings after he would have these harrowing night shoots in the desert, and then drive back to LA to deliver his kids to school.
"His character requires he goes to a very dark place, I have to examine my choices and my time and space but he really has to go places nobody wants to."
Now Aaron has left his menacing role behind, there was something new frightening him at the London premiere.
He said: "It's great to be in your home town showing the movie, but it makes me quite anxious, it's more daunting in England than anywhere else because I feel like it's my people and that is more scary.
"Here they are more honest and will tell you their opinions and sometimes they can be a bit brutal, but I think that is refreshing."
Nocturnal Animals, which also stars Jake Gyllenhaal, Michael Shannon and Isla Fisher, is released in UK cinemas on November 4.