Rossif Sutherland (Nostradamus) and Celina Sinden (Greer) met on the set of this show, fell in love, and are now married.
Mary, Queen of Scots,' real ladies-in-waiting were all called Mary; Mary Beaton, Mary Seton, Mary Fleming and Mary Livingston. Seton stayed with the Queen the longest, even in to her imprisonment by Queen Elizabeth. Seton lived long enough to see Mary's son become king of England.
Mary and Catherine are the only characters to appear in every episode of the series. Greer is credited for every episode, but there are some in which she does not appear, for example Succession (2016).
Although most of the important characters are real, a few key people are totally fictitious: Bash, Gideon Blackburn, the peasant Lucile, Narcisse, along with a dozen minor characters. Mary's four ladies of honor are based on the "four Maries," but have their own subplots and distinctive names. Of the real characters, perhaps the one that has had her personality and life story changed the most is Claude of Valois, who in real life married at the age of 11, had 9 children, died during childbirth at 27 and was not known for her intense romantic life and outward personality.
Francis mentions that many think he is weak and sickly because of a portrait that was painted of himself and his sister. The artist had Francis sit while his sister stood, making him appear very small in comparison. In real life, King Francis was very sick for much of his life.