The choice of casting raised eyebrows because Robbie, at 35, is older than Catherine Earnshaw, who is a teenager in the book; while Heathcliff is described by Brontë as being “dark-skinned”.
Speaking about Australian actor Elordi, Fennell said that she asked him to play Heathcliff after seeing him on the set of Saltburn and he “looked exactly like the illustration of Heathcliff on the first book that I read”.
“And it was so awful because I so wanted to scream. Not the professional thing to do, obviously.
“I had been thinking about making it and, it seemed to me he had the thing… he’s a very surprising actor.”
Robbie, meanwhile, is “not like anyone I’ve ever met – ever – and I think that’s what I felt like with Cathy”.
The Barbie actress, also from Australia, is “so beautiful and interesting and surprising, and she is the type of person who, like Cathy, could get away with anything”, Fennell said.
“I think honestly she could commit a killing spree and nobody would mind, and that is who Cathy is to me. Cathy is somebody who just pushes to see how far she can go.
“So it needed somebody like Margot, who’s a star, not just an incredible actress – which she is – but somebody who has a power, an otherworldly power, a Godlike power, that means people lose their minds.”
Despite taking some liberties, Fennell said she had retained much of Brontë’s original dialogue.
“I was really determined to preserve as much of her dialogue [as possible] because her dialogue is the best dialogue ever,” she said. “I couldn’t better it, and who could?”
Fennell’s Wuthering Heights will be released in cinemas on 14 February – Valentine’s Day – next year.