JK Rowling said she was "delighted" Johnny Depp had been cast in the Harry Potter prequel Fantastic Beasts And Where To Find Them.
The author said Depp, who faced domestic abuse accusations during his divorce battle with Amber Heard earlier this year, had done "incredible things" with his portrayal of dark wizard Grindelwald.
Depp, who vehemently denied the abuse allegations, appears briefly in Fantastic Beasts but is set for a more prominent role in the planned sequel.
"I'm delighted," Rowling said of Depp's casting at the film's world premiere in New York.
"He's done incredible things with that character."
Director David Yates said Depp - whose partner Heard filed for divorce in May - filmed his sequence in Fantastic Beasts in January and urged Harry Potter fans to trust the filmmakers about his casting.
"You have to trust us and see what he does in this movie," Yates said.
"You won't see very much in this movie because he appears in it very fleetingly. He appears much more in the second movie.
"What you have to remember about Johnny is that extraordinary talent and that talent never goes away.
"Hollywood is such a fickle place. People go up and go down.
"He's a huge Potter fan. He loves the world. He was beyond excited about working on this material. In fact he didn't even want to see a script, he just said 'I'm in'."
Rowling, who has been a vocal critic of Donald Trump, had earlier said she was in a "bleak mood" travelling to America to promote the film.
The author refused to speak directly about the president-elect at a press conference in New York but revealed the story of Fantastic Beasts was inspired by the rise of "populism".
"I think today is a day to focus on some good things and putting some good things out into the world hopefully," Rowling said.
"If you have read the Potter books, you'll know this period of history threatened to become very dystopian. You were looking at the rise of a very dark force.
"I conceived of this story a few years ago. It was partly informed by what I see as a rise of populism around the world."
She added: "Last night I was in a kind of a bleak mood boarding the plane and I thought I need to work.
"I got out the second screenplay and worked on that and it made me feel a whole lot better."
It has been reported that a sequel to Fantastic Beasts may feature a gay relationship between the character Depp's Grindelwald and a young Professor Dumbledore from the original Harry Potter stories.
Addressing the speculation, Rowling said: "I can't tell you everything I'd like to say because obviously it's a five-part story and there's lots to unpack in that relationship.
"I will say you'll see Dumbledore as a younger man and quite a troubled man because he wasn't always the sage. He was always very clever.
"We'll see him at what I think was the formative period of his life.
"As far as his sexuality is concerned, watch this space."
Rowling, who is currently working on a new novel, also revealed she hoped to bring the West End play Harry Potter And The Cursed Child to Broadway.
Fantastic Beasts And Where To Find Them is released in UK cinemas on November 18.