Pope Leo XIV calls for end to wars in Ukraine, Gaza

James Priestley has known Pope Leo XIV for decades, rooming with him in high school and attending Villanova University at the same time. He told ABC News it was "quite a shock" to learn his longtime friend had become the new pope.

At the same time, he said, "If you were going to imagine somebody to become pope, it would be Bob."

"He was a very religious guy, very bright guy and very organized," Priestley said. "I have no stories about him being bad in any way, shape or form from school."

Priestley said he saw his friend a few times over the years, but the pope was mostly out of the country. When Leo returned to the Chicago area last summer, Priestley said he got to see him at an event at St. Jude’s Church in New Lenox.

"I was very impressed," he said. "His public speaking ability is very, very good."

He said he also reconnected with Leo at that time at a pizza place in Homewood.

Priestley imagines Leo will make it back to the area again, this time as pope.

"I'm sure he'll be back to Chicago because this is his home base," he said. "This is where his brother Augustinians are located."

American-born Cardinal Robert Prevost was in the first grade when a neighbor told him he’d be the first American pope, his brother told ABC News.

Pope Leo XIV, the youngest of three boys who grew up in the Southside of Chicago, always wanted to be a priest, said his middle brother, John Prevost.

"He knew right away," John Prevost said. "I don't think he's ever questioned it. I don't think he's ever thought of anything else."

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The first American pope is being featured on a billboard in his home country.

An image of Pope Leo XIV standing on the center balcony at St. Peter’s Basilica after he was elected as the new pontiff was seen on a billboard in Philadelphia on Thursday.

“From the main line to the divine line,” the billboard states.

Leo, born Robert Francis Prevost, is a Chicago native.

Americans in St. Peter's Square said they were shocked and thrilled at the announcement of Pope Leo XIV, the first pontiff from the United States.

"It's so wonderful to just having experienced it, first of all," said Lisette Martinez, who rushed down to the square as soon as she heard there was white smoke. "And then it's the first American pope. It's surreal. It's holy. It's a blessing to be here."

William Jordan, from Virginia, brought his American flag down to the square.

"I blacked out for a second, truly," he said. "I don't even know what to think. I can't process it yet. Obviously, it's groundbreaking historically, and I have high hopes for what he can do in the Vatican and globally."

There were tears of joy for Jessica Wood as the new pope was announced. Wood, a New Yorker whose one-day trip to Rome just happened to coincide with this extraordinary moment in history, couldn't contain her joy.

"To be here for this moment is so unbelievably profound. It's something I'm going to be talking about for the rest of my life," Wood said.

-ABC News' Guy Davies, Zoe Magee and Maggie Rulli