John Lithgow teases details of Harry Potter series and playing Dumbledore

John Lithgow has shared rare details of the upcoming Harry Potter series as he prepares to play Dumbledore.

News emerged last month that the 79-year-old American actor had been cast as the iconic headmaster of Hogwarts School of Witchcraft and Wizardry in the forthcoming HBO adaptation of JK Rowling's Harry Potter book series.

While details of the new series are thin, Lithgow has shared some thoughts on the filming process - and teased how much screentime he might clock up portraying Albus Dumbledore over the projected seven seasons.

He told The Hollywood Reporter of the new series, "The overall concept of this entire reboot of Harry Potter is an entire season is devoted to a single novel."

He also signalled he may fly back and forth between the UK and USA while filming.

He said, "I mean, I was over in England for eight months for The Crown and barely came back (to the US). I think I may have come back once or twice. I imagine that I can come back much more."

He suggested the headmaster character may not feature hugely, teasing, "You know, Dumbledore is - he's kind of the nuclear weapon. He only goes on very, very occasionally. I don't think it's gonna be that hard a job, and, we'll just go back and forth."

Lithgow also revealed he has noticed a shift in his level of fame since his casting was announced last month.

He said, "Can you believe this has already started? The deal was only set, like, 48 hours ago, and in airports two weeks ago, somehow or other, people had gotten wind of this, and they were stopping me."