It took all day to set up the hunting scene, with Glenda Jackson in costume the entire time, as dog handlers and hawk handlers rehearsed their cues. The cameras finally rolled late in the afternoon, with the light beginning to fade and drizzle falling. The shot was perfect; everyone moved on cue. Unfortunately, one dog handler in a bright green shiny plastic raincoat released her hound, but forgot to stop where she was. She ran into the shot, ruining the take and wasting the entire day's shooting.
The film was released the same year as the miniseries Elizabeth R (1971), in which Glenda Jackson also played Queen Elizabeth I. In that production, Vanessa Redgrave's mother Rachel Kempson played Kat Ashley, Queen Elizabeth's governess during her childhood and the Lady of the Bedchamber during the early part of her reign.
Vanessa Redgrave (Mary, Queen of Scots) and Timothy Dalton (Lord Darnley) later played another married couple, Agatha Christie and Colonel Archibald Christie, in Agatha (1979). Although they never married in real life, they were in a relationship from 1971 to 1986.
Vanessa Redgrave was originally cast as Queen Elizabeth but was replaced by Glenda Jackson. She was later re-cast as the title character. Redgrave later played Queen Elizabeth in Anonymous (2011).
According to a 1974 interview, the role of Mary was intended for Geneviève Bujold. She turned it down after refusing to be typecast in movies about doomed sixteenth century Queens, leading to a major fallout with producer Hal B. Wallis. Oddly enough, her replacement, Dame Vanessa Redgrave, had appeared in A Man for All Seasons (1966) as Anne Boleyn, the same role Bujold had played in Anne of the Thousand Days (1969).