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Katy Perry performs at the Kids Inaugural concert for children and military families, one of the events ahead of the second-term inauguration of U.S. President Barack Obama in Washington January 19, 2013. REUTERS/Jason Reed (UNITED STATES - Tags: POLITICS ENTERTAINMENT) Image Credit: REUTERS

Watch out Beyonce and Katy Perry. There’s another diva set to perform during the inauguration festivities - Lady Gaga.

A person familiar with the inauguration tells The Associated Press that the pop star will perform at Tuesday’s ball for President Barack Obama’s staffers. The source spoke on condition of anonymity because that person wasn’t authorized to publicly reveal the information.

The staff ball is typically a private affair. During the last inauguration festivities, Jay-Z reportedly performed for that event.

According to one attendee, Jay-Z rapped a riff on one of his hit songs, “99 Problems but George Bush Ain’t One,” to the delight of the throngs of young staffers who worked to elect Obama in 2008.

President Barack Obama’s inauguration is shaping up to be an event as star-studded as any red carpet, with dozens of heavy hitters lining up to perform - and the promise of a few key surprises to liven up the weekend.

On Saturday, Usher sang “Yeah!” Katy Perry donned star and stripes for “Firework.” And a ballroom full of lucky kids got to rock out with Sasha and Malia Obama at Saturday’s Kids’ Inaugural Concert, a star-studded event that honors America’s military families.

“Now, inauguration is a pretty big deal,” first lady Michelle Obama, who hosted the event along with Jill Biden, told the assembled families at the Washington Convention Center. “But I have to tell you that my very favorite part of this entire weekend is being right here with all of you.” She paid tribute to the sacrifices that military families make, including their kids.

Pointing out that such kids often attend six to nine schools by the end of high school, always having to be “the new kid,” she said being a military kid meant “growing up just a little faster, and working just a little harder than other kids.” The concert was streamed live to several military bases around the country.

This was the second such concert for the Obama girls, and the choice of talent seemed to reflect the fact that they are four years older. While in 2009 they were entertained by Miley Cyrus and the Jonas Brothers, this time it was Usher and Perry, along with the groups Mindless Behavior and Far East Movement. Also performing were cast members from the Fox TV hit “Glee.”

Usher, in black leather, kicked off the proceedings with his hit “Yeah!,” followed by “Without You” and “OMG,” earning a huge cheer from the crowd. In between acts, there were kid-friendly diversions like a dance-off, or a race among mascots of the Washington Nationals: oversized versions of presidents like George Washington, Abraham Lincoln and Teddy Roosevelt.

Three members of the “Glee” cast were greeted warmly by the crowd: Naya Rivera, who plays Santana” Darren Criss, who plays Blaine” and Amber Riley, who plays Mercedes.

Nick Cannon emceed the evening, but it was Mrs. Obama, sporting her new bangs and wearing a white peplum shirt over black pants, who got to introduce the top attraction.

“It is now my pleasure to introduce the fabulous Katy Perry!” she said, and the singer emerged in what looked like a vintage swimsuit, covered patriotically with stars and stripes. She sang her hits “Teenage Dream,” ‘’Part of Me,” ‘’Wide Awake” and then “Firework,” which was accompanied by a slide show of President Barack Obama: Obama in the Oval Office, Obama exiting Air Force One, Obama greeting LeBron James.

“I’m very proud to be here ... and to see the Obamas and the Bidens here for four more years,” she said.

Perry was the favourite of concertgoer Dylan Garvin, 12, who came from Wilmington, Del. “I thought it was incredible,” Dylan said of the concert. “It’s a great way to celebrate.”

“I think it’s going to be the coolest thing ever to look back with my grandkids and go: ‘I was a part of that and I’m proud of that. I’m not ashamed of that,’” Clarkson said in a recent interview.

Clarkson once said she was a fan of Republican presidential candidate Ron Paul, but she says she voted for Obama twice. She’ll perform “My Country ‘Tis of Thee” at Obama and Vice President Joe Biden’s swearing in ceremony Monday after Obama takes the oath of office.

“We came up with a really cool arrangement for it and I really love the lyrics,” she said.

Beyonce will sing the national anthem and James Taylor will sing “America the Beautiful” on the West Front of the Capitol on Monday. Both performers are regular Obama supporters, and celebrities have been a big part of Obama’s strategy to attract voters. Bruce Springsteen is a regular supporter, as is Lena Dunham, Scarlett Johansson, Jay-Z and dozens of others.

Pop-rock trio fun., which had a wild year with two No. 1 hits, a near-platinum album and six Grammy nominations, also performed for first lady Michelle Obama, Sasha and Malia and Jill Biden on Saturday at the Kids’ Inaugural Ball.

“It’s been amazing year, and 2013 is kicking off with us doing the inauguration ... it’s just an incredible thing,” said lead singer Nate Ruess. “I think the three of us care so much about Obama and so to be invited, I can’t even deal.”

Fun. will were joined at the concert by Perry, Wonder, Keys, Usher, Smokey Robinson, Paisley, Marc Anthony, Mindless Behavior, Nick Cannon and the cast of “Glee.”

“I think they’re all very talented people. Stevie’s my brother and so is Usher,” Robinson said in an interview. “I know Katy ... I’m very happy to be performing among them.”

While there will be no shortage of star power, it’s not quite a repeat of the 2009 inauguration when everyone who’s anyone flocked to Washington for a televised concert on the Mall.

The first time around, Beyonce was a surprise guest, singing the Etta James classic “At Last” for the first dance. The Jonas Brothers - then favorites of the Obama girls - performed at the kids’ concert and U2, Springsteen and so many others performed on the Mall.

There may still be surprises in store, but plenty of performances are assured. Keys, Paisley, Chris Cornell, Jamie Foxx, Jennifer Hudson and Anthony will perform at the Commander-in-Chief’s Ball on Monday.

Will.i.am, who debuted the song “New Day” at 2009’s inauguration, will be at a number of events, including OurTime.org’s “General Now Party” on Saturday, which also includes John Legend and Common. Eva Longoria will host the “In Performance at the Kennedy Center” event, which celebrates Latino arts and culture, and will feature Antonio Banderas and Rosario Dawson. And 25-year-old pop party girl Ke$ha will perform a charity concert Monday.

The Creative Coalition will host parties Sunday and Monday that are expected to include Eric Stonestreet, Connie Britton, Taraji P. Henson, Melissa Leo and David Arquette, among others.

Like will.i.am, soul crooner Legend will attend multiple events, including Russell Simmons’ Hip-Hop Inaugural Ball II with 2 Chainz, Brandy and Pharrell. BET also has a ball that comedian-actor Wayne Brady will host” performers include Bell Biv Devoe, Doug E. Fresh, MC Lyte and Jermaine Dupri. And Pharrell will host an event late Monday that supports education.

Clarkson says she continues to gush when she thinks about all that’s going on to celebrate Obama’s second term in office.

“I’m excited to be a part of it honestly. I’m more stoked about (it more) than maybe a lot in my career,” she said.