Colin Farrell has reportedly been cast in the Harry Potter spin-off 'Fantastic Beasts and Where to Find Them'.

The 39-year-old actor - who's currently starring in the HBO series 'True Detective' - has been added to the star-studded line-up for eagerly-awaited movie, with Colin set to play the wizard Graves, according to The Hollywood Reporter.

He will star alongside Oscar-winning actor Eddie Redmayne and Katherine Waterson, with Eddie playing the lead role of Newt Scamander and the actress playing the female lead, Tina.

Meanwhile, 'Harry Potter' creator J.K. Rowling recently offered an insight into what fans of the original franchise can expect from the spin-off movie.

She previously posted to Facebook: ''Although it will be set in the worldwide community of witches and wizards where I was so happy for 17 years, 'Fantastic Beasts and Where to Find Them' is neither a prequel nor a sequel to the Harry Potter series, but an extension of the wizarding world.

''The laws and customs of the hidden magical society will be familiar to anyone who has read the Harry Potter books or seen the films, but Newt's story will start in New York, 70 years before Harry's gets under way.''