The 67-year-old actor has signed up for a "significant" role in the seventh series, but details of his character are yet to have been revealed, reports ew.com.
The actor's credits range from the films like Time Bandits, Brazil and Bridget Jones's Diary, to his Emmy-nominated title role on the series Longford, to a recurring role in the Harry Potter franchise (he played Horace Slughorn).
Jim has also won an Oscar in Best Supporting Actor category for his role in the 2001 film Iris.
The forthcoming seventh season is to be filmed in Iceland, Spain and Northern Ireland and the seven episodes, three short of the usual 10-episode series, will premiere next summer.
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