Diehard fans of the Harry Potter films will no doubt agree the role of Professor Remus Lupin could never be played by anyone other than the reedy, dishevelled, and very-British David Thewlis.
But the director of the beloved series, Chris Columbus, has revealed the late Robin Williams was a hopeful to play the new Defence Against the Dark Arts professor, in the third film, Harry Potter And The Prisoner Of Azkaban.
According to movie news site, Total Film, Columbus said: "I had a conversation with Robin Williams, who wanted to play Lupin.
"It was very difficult for me to say, 'It's all British. There's nothing I can do.'"
And it wasn't the first time WIlliams - who died in 2014 and is remembered for his roles in Jumanji, Mrs Doubtfire and Good Morning Vietnam - was turned down from securing a role in the franchise, first penned as a series by JK Rowling in 1997.
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In 2016 HuffPost reported Williams was also unsuccessful in securing the iconic role of Hagrid.
According to casting director Janet Hirshenson: "Robin had called [Columbus] because he really wanted to be in the movie, but it was a British-only edict, and once he said no to Robin, he wasn't going to say yes to anybody else," she said at the time. "It couldn't be."
Instead, Scottish actor Robbie Coltrane took on the gruff by kindly character, Hagrid, for all eight films.
As far back as 2001, Williams mentioned his attempt to land a role in the now billion-dollar fantasy franchise.
He told New York Post: "There were a couple of parts I would have wanted to play, but there was a ban on American actors," he said before adding:
"Maybe one day. Say if [Harry] goes to Yale and becomes president."