June 17 -- Feast of Saint Theresa of Portugal

Incest jokes are relatively tasteless.  That's why I'd never make them in a post like this.

Saint Queen Theresa

Saint Theresa was the daughter of King Sancho I of Portugal and Dulce of Aragon.  She married King Alfonso IX of Leon, whose mother, Urraca of Portugal, was King Sancho's sister.  Queen Theresa and King Alf-9 had three kids before the Vatican flagged the marriage as incestuous.

Who knew that first cousins counted as incest?  Obviously not the royal families of the Iberian peninsula in the twelfth century.  It was especially unclear to Alf-9, who subsequently married Berengaria of Castile, his first cousin (once removed).   They had five children before Pope Innocent III annulled the marriage.  In their defense, Pope Celestine had approved the marriage in spite of the consanguinity, but Innocent took a much tougher stance on marriage regulation.  The royal couple protested the annulment, but the only satisfaction they got was recognition of their children's legitimacy (and harelips).

King Alfonso IX

After her annulment, Theresa went back home and joined a Benedictine monastery.  She did some work there, converting it into a Cistercian convent that grew to more than 300 nuns.  She stayed put until the death of her former husband (I guess he actually never was her husband, since the marriage was annulled).  Alf-9 left his throne to her daughters, Sancha and Dulce.  Berengaria's son, Ferdinand, was put forward by his mom as an alternate candidate.

King Ferdinand III

The natural solution -- a marriage between Ferdinand and either Sancha or Dulce (or both) -- was unlikely to be accepted by the Vatican.  The second most likely resolution, civil war, seemed equally distasteful.  Theresa left the convent to talk to her daughters, persuading them to accept a big cash settlement in exchange for allowing Ferdinand to become the III.  Theresa and Berengaria civilly negotiated the settlement, which their children accepted. 

Peace having been secured, Theresa went back into the convent, took her final holy orders, and lived out her days as a nun.  Blessed are the peacemakers, for they will be called the children of God.  Matthew 5:9.