There have been 13 popes named Leo in the history of the Roman Catholic Church but perhaps none of them was as famous as the Leo who entered the Vatican on Thursday - Hollywood star Leonardo DiCaprio.
DiCaprio, who is known as Leo, was received by Pope Francis, the Vatican said, without giving details.
But the one-line announcement was enough to send photographers and television crews scrambling to stake out the Vatican's gates to try to catch him coming out.
DiCaprio, speaking Italian, thanked the pope for receiving him and then, switching to English, gave him a book of paintings by 16th century Dutch painter Hieronymus Bosch.
Pointing to one painting, DiCaprio told the pope it had hung over his bed as a boy and said "through my child's eyes it represented our planet.
Footage issued later from Vatican television showed that the audience was connected to their mutual concern about the environment and climate change.
"It represents to me the promise of the future and enlightenment and it is representational of your view here as well," he said. He later gave the pope a check for an undisclosed sum which appeared to be a donation for papal charities.
Last week, the 41-year-old Oscar nominee was honored at the 22nd Annual Crystal Awards held at the World Economic Forum in Davos for his foundation's support of conservation and sustainability projects.
The pope wrote a major Catholic Church document known as an encyclical last year in defense of the environment and has often said that time was running out for mankind to save the planet from the potentially devastating effects of global warming.
The pope gave DiCaprio a copy of his encyclical and asked the actor to pray for him.