WHEN Gov. Corbett visited Rome in March to lobby for Pope Francis to come here for the World Meeting of Families in September 2015, he didn't expect a firm promise.

Then the pope whispered, "I will come."

But the Vatican swore Corbett to secrecy, telling him to keep mum until they decided to officially announce it. Like a good Catholic, Corbett obeyed.

About 9:30 a.m. yesterday in Rome (3:30 a.m. our time), the news became official: The pontiff announced his plans to visit Philadelphia to religious leaders - including Archbishop Charles Chaput - gathered in Rome for a summit on marriage and family life.

"Typically, a 3:30 a.m. phone call is not a good thing," first lady Susan Corbett said with a laugh. "But in this case, Tom and I were so excited to receive the news the Holy Father has confirmed his attendance at the World Meeting of Families."

The first lady joined Mayor Nutter and other city and church leaders to celebrate the announcement at the Philadelphia Museum of Art, where an army of excited Catholic school students filled the grand hall's staircase.

It was great fanfare for "news" that surprised few. The pope's whispered promise aside, the Vatican has been dropping hints for months that Francis would come, and his predecessor, Benedict XVI, had promised it.

Still, the confirmation sent a jolt of anticipation through devout Catholics.

"How can you not feel good about it? It's great," said Paul Prettyman, 68, of Washington Township, Gloucester County, who attended the noon Mass at the Cathedral Basilica of Ss. Peter and Paul at Logan Circle.

Natalie Nkurunziza, 32, a Harrisburg resident who works in Philadelphia and spent her lunch break at Mass, agreed: "I heard the news this morning. I'm super-excited!"

The pope's three-day visit will cap a six-day event that begins Sept. 22 and is expected to draw more than 2 million faithful to Philly. Pope Francis will attend the Festival of Families on Sept. 26 and give a public Mass on Sept. 27, both on the Benjamin Franklin Parkway, organizers said.

"The Holy Father's charisma, presence and voice will electrify our gathering," Chaput said in a statement from Rome.

More than 100 speakers are expected at sessions addressing topics like virtue, discipline, divorce, interfaith marriage, infertility and homosexuality. Registration opened last week online at worldmeeting2015.org.

"This will be the largest event in the city's modern history," Mayor Nutter said.

Such a huge event also means a huge price tag: $45 million, organizers project. Fundraising is underway, with more than half already in pocket, organizers said.

Where do 2 million people sleep? Organizers say they've put hotels from here to Delaware and New Jersey on alert, and they're recruiting families to open their homes to visitors, as well.

As for who gets to put the pope up overnight, organizers aren't sure about that, either.

"Generally, he stays with the host," said Robert Ciaruffoli, president of the World Meeting of Families.

The host would be Chaput. But with a world leader as a houseguest - and the sprawling entourage sure to accompany him - the papal sleepover's location remains under seal, at least for now.

Not that organizers expect any trouble, Nutter assured the Art Museum crowd. Security is sure to swarm the city. The pope's visit will include city, state, Vatican and Italian police; FBI and Secret Service agents; and the Swiss Guard, Nutter said.

The Philly visit will be Pope Francis' first to the United States, and he'll be just the fourth pope to visit the country. The most recent papal visit was Pope Benedict XVI's trip to New York and Washington in 2008.

The World Meeting of Families, held every three years, aims to strengthen family bonds and is the world's largest Catholic gathering of families. Next year's meeting will be the first held in the United States.

Tom Fetters, 53, of Northern Liberties, hoped the meeting's message would resonate through the area.

"There's a lot of single parents and a lot of families who are struggling," Fetters said. "I hope his message can bring people together."

On Twitter: @DanaDiFilippo

Blog: phillyconfidential.com