'Harry Potter' series may be more satisfying as it stays closer to books, says Gary Oldman

The upcoming television adaptation of JK Rowling's "Harry Potter" books could be more satisfying for audiences because it will be able to stay closer to the source material, actor Gary Oldman has said.

Oldman, who played Sirius Black in four "Harry Potter" films, said the movies had to leave out substantial portions of the books because of their runtime, resulting in considerable character detail being lost.

"We had to cut a lot (for the 'Harry Potter' movies), and still we could only get the films down to, like, three hours," Oldman told Entertainment Weekly in an interview.

"A lot of character detail was sacrificed," he added, saying he believed the HBO series would adapt the books "pretty much word-for-word", which he felt could make it more satisfying for viewers.

Despite the omissions, Oldman said he remained proud of his association with the hugely successful film franchise.

"I'm proud and grateful to have been part of the 'Harry Potter' films because it is such a phenomenon, the like of which I don't think you're ever gonna see again," he said.

The actor also credited director Chris Columbus, who helmed the first two films, with establishing the wizarding world and bringing together the original cast.

"We were extraordinarily lucky to have those people come back again, and again, and again, and literally grow into those roles," he said.

Oldman has previously said that Sirius Black, a character he particularly liked, did not receive enough screen time in the films.

The character first appeared in "Harry Potter and the Prisoner of Azkaban" and was killed in "Harry Potter and the Order of the Phoenix", released in 2007.

The first season of HBO's "Harry Potter" series has wrapped and is scheduled to premiere on HBO and HBO Max on December 25. The second season, based on the second book in Rowling's series, is currently in pre-production at Leavesden Studios outside London.

The new series stars Dominic McLaughlin as Harry Potter, Arabella Stanton as Hermione Granger and Alastair Stout as Ron Weasley. The cast also includes John Lithgow as Albus Dumbledore, Janet McTeer as Minerva McGonagall, Paapa Essiedu as Severus Snape, Nick Frost as Rubeus Hagrid, Rory Wilmot as Neville Longbottom and Lox Pratt as Draco Malfoy.

Oldman will next be seen in the sixth season of Apple TV's "Slow Horses", which premieres on September 16.