We don't yet know Harris's role, but some of his best roles have been villains, including Moriarty to Robert Downey Jr's Sherlock Holmes in "A Game of Shadows" and the diabolical David Robert Jones in sci-fi series "Fringe."
Filming wrapped in May, so perhaps Harris will only be lending his voice to the film?
As ScreenRant points out, former Doctor Who Matt Smith is also in final talks to join the film at this late date.
Harris's father was Richard Harris of "Gladiator," "Harry Potter," and "Camelot" fame.
His credits include "Mad Men," "The Curious Case of Benjamin Button, "The Man from U.N.C.L.E." and "The Expanse." He'll also be in the upcoming HBO miniseries "Chernobyl" and "Carnival Row" on Amazon with Orlando Bloom.