Nostradamus' Prophecies were the visions of the future that Nostradamus had as the court seer.
Background
Nostradamus began having visions in the Pilot when he told Queen Catherine that Mary's presence would cost Francis his life. These visions continued until The Consummation when the Queen no longer trusted the visions of Nostradamus so deeply.
Season One
In Kissed at King Henry's command after he inquires why Nostradamus is always whispering in the Queen's ear, and tells him that a seer in Prague can tell the future with cards; Nostradamus tells Henry that his power does not work that way. He tells the fortunes of Queen Mary and her ladies in waiting after they each draw a card: Mary's fortune is "The lion will fight the dragon on the field of poppies", Greer's fortune is"You will fall in love with the man with the white mark on his face", and Aylee's fortune is "You will never go home". Mary asks Nostradamus why he would scare her friends like that, because she knows that Catherine had nothing to do with it. She asks who he serves, and Nostradamus says he only serves the realm, himself and the truth.
When Sebastian is injured he is brought to Nostradamus, who sees his vision again and understands that the war was brought into the castle through the attack on the French troops and Sebastian.
In A Chill in the Air Nostradamus warns Bash to stay close to the castle, or he’ll be in grave danger.
In Fated Nostradamus discusses with Catherine about the prophecy of Francis. He claims he the prophecy hasn't changed and the Francis will die if he is wed to Mary. Later Nostradamus sees another prophecy of death in the castle and he tells Mary of what he saw. Mary shares with her ladies-in-waiting that he said one of them would die before the first frost falls. When the death occurs, it is Aylee. She claims Nostradamus was right and she will never be going home. Mary then calls Nostradamus the devil. Nostradamus knows that Catherine couldn't have possibly done this, so he leads the trail straight to Clarissa. As Nostradamus chastises her for what she has done, he removes her bag of her head and makes her look Aylee in the face. Clarissa is forced to look Aylee in the eyes.
In The Consummation, After Mary kills Clarissa to save the lives of Catherine's youngest sons, the prophecy is apparently fulfilled since Clarissa turned out to be the Queen's firstborn and not Francis. Nostradamus' sees a new vision which is of Mary and Francis: happily married years beyond their union and even having children. He tells Catherine about the change in his visions and she goes through quite the range of emotions before settling on anger when he suggests her life might be saved now since she’ll no longer oppose Francis and Mary’s union. It’s gone past her standing in the way; she’s been found guilty of adultery and treason therefore she is condemned to die and has a lot to worry about. She warns Nostradamus that if she can’t turn things around she’s going to make sure he burns before she’s executed.
However, Clarissa is revealed to still be alive and Nostradamus’ vision changes again by the end of the episode to include Francis’ historically accurate death of an ear-related disease, but he does not tell Catherine who is in a wonderful mood due both to her son’s happy union and her own pardoning.
Season Two
In Drawn and Quartered, When Queen Catherine visits Nostradamus in the dungeons, where he is awaiting death after being accused of killing Lord Narcisse's son Eduard; she tells him that unfortunately she doesn't have a plan to help get him out of this. Nostradamus is quite angry to hear this after everything he has done for her, and he tells her that if she thinks that her sins will stay buried then she is sadly mistaken; he also hints at the possibility that Clarissa may still be alive. However Catherine doesn't get a straight answer from Nostradamus when she inquires as to exactly what he means, since the guards come to take him away before he can say anything further.
Season Three
In In a Clearing, When Nostradamus tells Queen Catherine of a new vision he has had about Francis' fate, the Queen is worried about her son and after listening to the vision asks what can be done to keep her son safe. Unfortunately Nostradamus has nothing to tell Catherine and urges her to get Francis to listen to her or else he may die.
Later after finding Francis dead under a tree in the woods surrounded by white petals just as he predicted, Nostradamus helps bring Francis' body back to French Court.
The next day at the funeral, Nostradamus tells Catherine that he has no intention of staying at Court; however he gives his old friend one last vision: Only with the help of her daughter in law will she be able to rule France and become Regent.
Gallery
<gallery type="slideshow" position="center" widths="500"> Normal_Reign_S01E08_Fated_1080p_KISSTHEMGOODBYE_1486.jpg|frame|left|Everyone finds Aylee dead as Nostradamus predicted Catherine_&_mary6.jpg|Francis is found dead in a clearing as Nostradamus predicted.