The film's production company said on Friday that Philipp von Schulthess, who is a grandson of Count Claus von Stauffenberg, would play the role of a 1944 German Army adjutant in the film "Valkyrie," which began shooting this week.
Last month, the late hero's son Berthold von Stauffenberg forecast the film would be "rubbish" and said it was "not nice" that a "practicing Scientologist" was playing the part of his father.
German politicians have continued to assail Cruise's philosophy of life as harmful, outraging US commentators who said he was being victimized on account of his creed.
A US-German co-production
The shooting of "Valkyrie" began at the Babelsberg Studios near Berlin on Thursday
The film, directed by Bryan Singer, 41, is a joint production by US and German studios and has qualified for 4.8 million euros ($6.6 million) in grants from Germany's film industry board.
It was not known Friday how Schulthess came to be in the cast, but it appeared he had attended an audition.
Studio Babelsberg also disclosed that Hitler would be played by British actor David Bamber, who played a Bob Geldof look-alike in the movie "I Am Bob" earlier this year.
The production company said Cruise was present during the second day of filming.Not exactly a perfect match
On Friday, the 63rd anniversary of the July 20 coup attempt, German newspapers reviewed other reasons why Cruise, 45, might make a poor plotter such as the age difference: Stauffenberg was 36.
The mass-circulation Bild noted that Stauffenberg was about 1.85 metres tall and Cruise less than 1.70.
Officials deny that Scientology was the reason rules were not relaxed to allow location shooting in a government office building where Colonel Stauffenberg had his office and was summarily shot by the Nazis.
Germany, which bans anti-democracy groups and monitors neo-Nazis, keeps Scientology under surveillance.
Junior politicians have continued to attack Cruise.
"Stauffenberg risked his life for freedom," said Rudolf Köberle, state secretary for interior issues in Baden-Wuerttemberg state. "It sullies his heritage to have a Scientology adherent act him."
Germans have been criticizing Cruise since 1996 when the actor played in "Mission Impossible."