In the movie Harlan mentioned an affair of Goebbels with a Czech dancer. This is an actual event from 1938, where Goebbels fell in love with Lida Baarova, who was starring in the German 1938-movie "Der Spieler", playing Nina, General Kirileff's daughter. Goebbels called Baarova a "complete beautiful woman" and was even thinking about getting divorce from his wife Magda, who herself had an affair with another man. After Magda asked advice by Hitler he refused it, also because the German army was planning invading the Sudetenland in that moment. After a personal talk between Hitler and Goebbels, he took the divorce request back, which made Lida Baarova to a Persona non grata. However according to Czech sources Baarova didn't wanted it this affair but had no choice, as she was afraid of Goebbels and his love letters where he described himself and her as Adam and Eve living on an island. In later talks Goebbels always denied an affair with Baarova.
The discussion between Harlan, Goebbels and Marian in the propaganda ministry is described very detailed in Veit Harlan's autobiography "Im Schatten meiner Filme" (In the Shadows of my movies) from 1966. The lines that were used in the movie are exactly the same as in the book. The differences is that Harlan remained in the room and Marian didn't refuse the role in the actual room. Instead he was heard screaming "Tell Herr Minister: I'll do it."
The Othello stage adaptation at the beginning of the movie was actually performed and had it premiere in June 1939 at the "Deutsches Theater Berlin", starring Ferdinand Marian as Jago, directed by Erich Engel. The character of Othello, which was played by fictitious actor Wilhelm Deutscher in the movie, was in real life portrayed by Ewald Basler (1898-1978).
In the scene where Goebbels, Harlan and some other people are watching a movie on Goebbels' 43th birthday, they are watching an actual birthday home movie with the real children of Goebbels. This movie was made a few days before his birthday by Heinz Rühmann, who was invited by Goebbels himself 1940 to his villa in Wannsee near Berlin. Goebbels liked Rühmann and let him playing many movies but Rühmann himself wasn't a Nazi.
Karl Markovics was first set to play Joseph Goebbels. He later got to play the role in Lída Baarová (2016).