Exultavit cor nostrum is a letter, also known as a Papal bull, from Pope Urban IV to the Mongol Ilkhanate leader Hulagu in 1263/1264.
According to John, Hulagu desired to become a Christian, and requested that Urban send a representative who would help to baptise him.
[2] He cautiously welcomed Hulagu's envoy, and announced that William II of Agen, Latin Patriarch of Jerusalem, would be investigating further.
[4] A few years later, Franciscan William of Rubruck travelled to Karakorum, and took part in a formal debate at court between Christians, Buddhists and Muslims, to determine which faith was correct.
According to the historian Jean Richard, its wording "bore signs of the intermediary of a western scribe, probably the Ilkhan's Latin notary, Rychaldus."