John Lithgow has admitted playing Albus Dumbledore in the 'Harry Potter' reboot series will likely be his final "major role".

The 79-year-old actor has been cast as the Hogwarts headmaster in the upcoming HBO adaptation of J.K. Rowling's magical book series and one of the reasons why he accepted the job was because he saw it as a good way to start "winding down" his career.

He told the Sunday Times' Culture magazine: "Of course, it was a big decision because it's probably the last major role I'll play. It's an eight-year commitment so I was just thinking about mortality and that this is a very good winding-down role."

After accepting the role, John was surprised to receive a backlash because of the project's ties to the author, who has caused controversy with her advocacy for single-sex spaces and women's rights, which have been viewed as anti-trans by some.

Showing some of the messages he received, he said: "I thought, why is this a factor at all? I wonder how JK Rowling has absorbed it. I suppose at a certain point I'll meet her and I'm curious to talk to her."

Asked if the comments he'd received had made him have second thoughts, he added: "Oh, heavens no."

And after playing the late Roald Dahl in stage show 'Giant', John is baffled no one has questioned his association with that children's author because of his anti-Semitic comments.

He said: "No one complained when I agreed to play Dahl, but I've received so many messages about JK Rowling. Isn't that odd?"

John confirmed his 'Harry Potter' casting in February, and admitted it was a "hard decision".

He told ScreenRant: "Well, it came as a total surprise to me. I just got the phone call up at the Sundance Film Festival for yet another film, and it was not an easy decision because it's going to define me for the last chapter of my life, I'm afraid. But I'm very excited.

"Some wonderful people are turning their attention back to Harry Potter. That's why it's been such a hard decision. I'll be about 87 years old at the wrap party, but I've said yes."