Stars Come Out to Cheer Madonna & Britney

When Madonna and Britney Spears take the stage together, they have a history of creating memorable moments, like the 2003 MTV Video Music Awards, where the superstar pairing heated things up with a three-way, all-girl smooch with Christina Aguilera.

So when it was announced on Wednesday that not only was Brit planning on joining the Material Girl on stage at her Thursday night concert in L.A., but that Britney's ex, Justin Timberlake would be performing too — everyone was wondering if the former lovers would be seen together for the first time in years.

Alas, a Britney/Justin reunion was not in the cards as the onetime paramours each performed separately with Madonna.

CLICK HERE for OK!'s Ultimate Britney Gallery!

First up was Brit, who came out onto the stage at Dodgers Stadium to lend her voice to Madonna's 1994 hit, "Human Nature." The celebrity-filled audience, which included Heidi Klum, Jennifer Lopez, Drew Barrymore, Kate Moss, Ryan Seacrest, Fergie, Lucy Liu and Elizabeth Banks, erupted into applause as the 26-year-old mother of two sang in public for the first time since her disastrous performance at the 2007 VMAs.

"This was a completely different Britney from a year ago," one concertgoer told OK! after the show. "She was glowing! It looked like she actually wanted to be on the stage."

Dressed conservatively — especially by Britney's standards — the "Womanizer" songstress displayed a real onstage chemistry with Madonna, who welcomed her to the stage by slinging an arm around Brit's shoulder. "They were really vibing off each other," says another fan.

And their kinship was made even more evident when Madonna told the crowd, "She is not your [expletive]," which elicited a laugh from Britney, who added her now-signature, "It's Britney, [expletive]." As Brit made her exit, Madge gave her a tender smooch — on the hand.

CLICK HERE for OK!'s Ultimate Madonna Gallery!

About an hour later, it was Justin's turn to join Madonna for a song. The "SexyBack" singer was on hand to help Madge out with the song, "4 Minutes," that they recorded for her Hard Candy album. And now that Madonna's single again, the 50-year-old hottie had no problem getting physical with her singing partner.

"While he was singing his part, she strutted over to Justin and began grinding on him," one audience member recalls to OK!. "He didn't seem to mind. In fact, he had a really mischievous grin on his face."

We can only hope that Madonna's alleged man-friend, baseball stud Alex Rodriguez wasn't getting too jealous as he watched the show from the front of the audience.

"Alex seemed to be enjoying himself," says a Madonna fan who spotted A-Rod in the crowd. "He was moving to the music and he was definitely paying attention to Madonna on the stage."

By Patricia Ramos