The 1572 papal conclave (May 12–13), convoked after the death of Pope Pius V, elected Cardinal Ugo Boncompagni, who took the name Gregory XIII.

Also, king Philip II of Spain opposed Farnese's candidature because he considered his elevation dangerous to the balance of power in Italy.

[6] The first step taken by Granvelle was to inform Alessandro Farnese that the King of Spain would not accept his election and to ask him to withdraw his candidature in order to maintain peace in Italy.

Surprised, Farnese understood that with such strong opposition, he would never obtain the required majority, but, admitting his defeat, he wished to be able to use his influence effectively in the choice of the new pontiff.

[7] Almost the whole next day leaders of the main factions: Farnese, Bonelli, Granvelle and Borromeo, spent looking for a compromise candidate and finally agreed to elect the 70-year-old Ugo Boncompagni.