Anthony Hopkins had previously portrayed C.S. Lewis in Shadowlands (1993) 30 years prior to this film.
The waltz, called "And the Waltz Goes On" that is played right before the end cards was composed by Anthony Hopkins.
Both Anthony Hopkins and Matthew Goode were at the time of this film's release only a few years older than the characters they were playing Sigmund Freud and C.S. Lewis, Hopkins being 85 to Freud's 83, and Goode being 45 to Lewis' 40.
By contrast, the actresses Orla Brady and Liv Lisa Fries are both considerably younger than the characters they play, Janie Moore and Anna Freud, Bradie being 62 to Janie Moore's 77 and Fries being 33 to Anna Freud's 44.
The film based on the stage play of the same name by Mark St. Germain, which is in turn based upon the non-fiction book "The Question of God" by Armand Nicholi. The book also inspired a non-fiction documentary by that name on PBS. The book and documentary compare the lives and ideas of Lewis and Freud but unlike the play and this film do not postulate an imaginary meeting of the two men.
The play is simply confined to their conversation, while the film expands the play by showing scenes from the outside personal lives of Lewis and Freud.
The closing credits have multiple title cards explaining things that happened to both Lewis and Freud after the events of this film. They mention that during World War II, Lewis housed children being evacuated from London during the Nazi air raids. They do not mention that one of these was Jill Flewett, who later married a grandson of Sigmund Freud, Clement Freud.