Pope Francis surprised many people in Italy on Tuesday when he described Rome Mayor Ignazio Marino as someone who only "pretends to be Catholic."

"He pretends to be Catholic, it came on him all of a sudden. It doesn't happen like that," Pope Francis said.

During his flight back to the Vatican from the United States and Cuba, the Pope was asked if he invited Marino for his trips since he was spotted in Philadelphia, according to News Max. 

The Pope replied: "I didn't invite the mayor. Is that clear? I asked the organisers and they didn't invite him either."

Pope Francis reportedly dislikes Marino because of the latter's vocal support for gay marriage and euthanasia—two causes that the Roman Catholic Church strongly opposes.

Despite his supposed non-invite, Marino was still seen on the last leg of the papal tour, fresh from his vacation in the US and the Caribbean. Marino insisted that he was there not as a guest of the Pope but of the city of Philadelphia.

The Italian media had a field day with Pope Francis' strong views against Marino. "If the most popular man in the world takes down one of the least popular in Italy, that says that all the rules of the game have been thrown up in the air, including possibly those of mercy," said the Turin daily La Stampa.

"The Pope excommunicates Marino," the right-wing Roman daily Il Tempo wrote in its headline. Il Giornale, owned by former premier Silvio Berlusconi, highlighted Marino's "colossal shame."

Pope Francis' dispute with Marino will not make things easy for Rome to prepare for the Year of Mercy this December, which will probably welcome around 20 million pilgrims who will be granted special indulgences, which is the highest form of forgiveness.