The 69-year-old actor, famous for playing Dr. Alan Grant in Jurassic Park, revealed he filmed a secret role for the third instalment in the superhero trilogy, starring Chris Hemsworth as the Norse god, during a recent interview with ShortList.

"I'm not really allowed to say this and I can't tell you what it is... I did a couple of days on Thor just before I came over here," Neill said, jokingly adding he had "to sign all sorts of things" to promise he wouldn't talk about the film or his role in it before shooting his scenes.

"So if I say anything else, Marvel’s secret agents - and they are lethal - will come and get me and probably my children, as well."

Neill reunited with his Jurassic Park co-star Jeff Goldblum, who plays The Grandmaster, in the Marvel film.

Tom Hiddleston is returning to the movie as Thor's villainous brother Loki, Idris Elba stars as Heimdall, and Sir Anthony Hopkins reprises his role as Odin. New additions to the cast also include Cate Blanchett as Hela and Karl Urban as Skurge, while Mark Ruffalo appears as his Avengers scientist Bruce Banner and his monstrous alter ego The Hulk.

Plot details are currently under wraps, but the title suggests the film may follow the story of an apparent apocalypse. In Norse mythology, Ragnarok is a series of events, including a great battle, which ultimately result in the death of Norse gods including Odin, Thor, and Loki.

Thor: Ragnarok is slated for release in November, 2017.