The 45-year-old actor plays a young Professor Albus Dumbledore in and admits it was a great ''comfort'' to find out Rowling was supportive of his casting.
He said: ''When the boss says, 'I like you,' it gives you a little bit of comfort. You can't help but step into something like this, playing a part like this without feeling a sense of responsibility, a fear of letting someone down. But when the creator gives you the thumbs up, it's a blessing.''
And his co-star Eddie Redmayne - who plays Newt Scamander in the movie - praised Jude's ''formidable'' acting skills.
He added: ''He is a formidable, formidable actor with great gravitas and weight and yet at the same time, he has this kind of playful quality. And I'll never forget our first scene, which was the first time we see each other in the film.
''I just saw his back, basically. And the way he turned around, it was instant. It was like, in one look, he had managed to inhabit that. I hadn't had any expectations about Dumbledore. But somehow it was solidified in one look.''
Meanwhile, Rowling previously revealed bringing Hogwarts back to screens in 'Fantastic Beasts: The Crimes of Grindelwald' was ''beautiful''.
She said: ''We had to go to Hogwarts, because that's where Dumbledore is and he's kind of important in the 'Fantastic Beasts' story, so yeah we had to go back there. I wasn't sorry to go back, it was beautiful.
''[Jude's] extraordinary. I couldn't have wished for better, he's amazing. I told Jude more than anyone knows except me. Jude knows a lot now.''
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