St. Louis, King of France, asked one of his nobles named Joinville what he would do if he were asked to choose between committing a mortal sin and being struck with leprosy.
Joinville, without any hesitation, answered the King: “I would sooner commit ten mortal sins than be infected even once with that terrible plague.” 
The King looked sadly on his friend and said: “Ah! my dear sir, it is evident you do not know what an evil it is to commit a mortal sin. There is no evil so terrible as sin is: for no matter how much we detest our sins, we can never be sure so long as we live whether or not God has forgiven us, or that we have sufficiently repented of them.”
Rev. D. Chisholm, The Catechism in Examples (London: R & T Washbourne, Ltd., 1919), 382.
Short Stories on Honor, Chivalry, and the World of Nobility—no. 369
