The Pope last month welcomed Xavier Bettel, Luxembourg's openly gay prime minister, and his husband Gauthier Destenay to the Vatican.

Bettel was among the European leaders gathered at the Vatican to celebrate the 60th anniversary of the signing of the Treaty of Rome.

The couple was greeted at the Vatican by Archbishop Ganswein, Pope Emeritus Benedict XVI's personal secretary, according to the AFP.

“It was a great pleasure and honor to me and Gauthier to be welcomed by the leader of the Catholic Church. XB,” Bettel tweeted.

Bettel and Destenay entered a civil partnership in 2010 and married in 2015, taking advantage of legislation ushered in by Bettel's administration.

(Related: Luxembourg PM Xavier Bettel: First EU leader to marry same-sex partner.)

Bettel is currently the world's only openly gay head of government, though Iceland and Belgium have also had openly gay prime ministers.