The cast of Fantastic Beasts And Where To Find Them were unaware of JK Rowling’s plan to make five films in the series before she revealed the news to fans, one of the movie’s stars has said.

Eddie Redmayne and co-star Katherine Waterston unveiled unseen clips from the upcoming Harry Potter prequel at Entertainment Weekly’s PopFest in Los Angeles.

Earlier this month, JK told fans in London she had planned scripts for at least four further Fantastic Beasts films.

Katherine, who plays Porpentina Goldstein, said JK told her “some really exciting details about the next film” but the author had not mentioned her intention to make another four movies.

“When she said we were doing five, that was news to us,” Katherine said. “There’s so much going on that we’re not privy to.”

Eddie, who plays the lead role of Newt Scamander, said of JK: “It’s her imagination. She has such a passion for it and a specific story she wants to tell. We get glimpses into that … it’s exhilarating when it happens.

“Fantastic Beasts – the title – and Newt and his beasts are a way into this world. There’s a bigger story about good versus evil that she wants to tell.

“You haven’t seen much of it in the trailers and the clips of the film but it’s really at the core of the story she’s telling. I do see that it’s a macro-story that could take more time.”

Eddie also revealed he spent time with an expert who tracks animals to help prepare for his role.

“I went and met this dude who tracks creatures for a living,” he said.

“He took me into this forest and showed me all these grasses and herbs that were antidotes.

“I said (on set): ‘Well this guy does all this stuff, rubbing herbs together and spitting … they were like ‘use it’.”

Fantastic Beasts And Where To Find Them is released in UK cinemas on November 18.