The following reads like it is impossible or untrue but there is nothing to suggest that it is untrue. The fact that the person you are about to read about was very much in the public eye, being a Queen and that it was known she could not become pregnant, suggest that this story is in fact true.

This is a summary of page 74 of the Secret of the Rosary by St. Louis De Montfort:

The Queen of France, Blanche of Castille, was deeply grieved because after 12 years of marriage she was still childless. Saint Dominic visited her and advised her to say the rosary evey day to ask God for the grace of motherhood. She listened to his advice and said the rosary every day. In the year 1213 she gave birth to her eldest child, Philip, but the child died in infancy. The Queen, who must have been heartbroken, obviously did not blame God since she increased her prayer life and asked for our Lady’s help more than ever before. She actually had a large number of Rosaries given to all members of the royal court and to to people in several cities in the kingdom and asked them to say the rosary so that she would be blessed with another child. In 1213, Blanche of Castille, Queen of France, gave birth to Saint Louis.

 comments please.