Hugh Grant “drove (his) family mad” by embarking on a deep dive into his Heretic character for months before the shoot.

For the thriller, the ’90s heartthrob transformed into the creepy and sinister Mr. Reed, who traps two Mormon missionaries in his home and tests them on their religious beliefs.

Grant revealed on BBC Radio 2 on Wednesday that he dug deep into his character for months before filming began and created mood boards and a full biography as part of his prep.

“I did dig deep, deep, deep into the character. This guy is espousing some quite complicated arguments and I really wanted to get into those. That’s what I did for months and months and months and drove the family mad,” he shared.

“There are mood boards then copious spidery notes all over the script and then there’s a huge biography that expands and mushrooms over the months. (It gets) bigger, bigger and bigger until I can tell you almost anything that happened on any birthday of this character, decades before he was born. I know, it’s bonkers.”

The Notting Hill actor, who shares three children with his wife Anna Eberstein, explained that he does “an absurd amount” of character work because it makes him feel “marginally less panicked” when the cameras start rolling.

Elsewhere in the interview, the British actor praised his “unnervingly good” co-stars Sophie Thatcher and Chloe East, who play Sisters Barnes and Paxton, for maintaining a state of terror throughout the film.

“Twenty minutes into this film, they have to start looking a bit scared and then just get more and more scared for another hour and 10 minutes and that’s hard. Brutally hard. I can’t imagine how they did it,” Grant said.

Heretic will be released in U.K. cinemas on Friday 1 November.

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