The show even killed off the popular character of King Francis II because his death was such a pivotal moment in the life and leadership of the real Mary back in the 16th century.
Reign may well end the show in a way that honors the Mary, Queen of Scots from the history books.
Even though a lot of the events over the years have been fantastical departures from the history books, Reign has often stuck to the key moments.
Of course, the ending for Reign may have been planned out from the beginning.