The pope will meet Erdogan on Monday, February 5 at the Vatican. It will be the first time a Turkish president will come to the Vatican in 59 years.
The reason for this unexpected meeting seems clear enough: both disagree with Trump's decision to recognize Jerusalem as Israel's capital. The announcement has generated enormous tensions in the Middle East.
In addition to this topic, the two leaders will also likely discuss the situation in Syria and the Kurdistan crisis.
Relations between Turkey and the Vatican have gone through severe crises, especially after Pope Francis called the massacres the Young Turks carried out against Armenians in the Ottoman Empire 100 years ago a 'genocide.'
There were also great tensions between the Holy See and Turkey after Benedict XVI's speech in Regensburg in September 2006.
Pope Francis and Erdogan already met face-to-face in November 2014, when the pope visited Turkey. After visiting the Vatican, Erdogan will travel to several countries in Latin America.