Britney and Justin at Madonna Concert

Britney and her former lover boy Justin performed at Madonna's Sticky & Sweet tour at L.A.'s Dodger Stadium Thursday night. They didn't exactly reignite their old romance, a they appeared at the stage separately. But, PEOPLE has learned, the two actually crossed paths during rehearsal. Timberlake was first, and then Spears came on stage to run through her part. "They said 'hi' to each other. Justin was very cool," a source says.

Britney was also seen watching Justin during his sound check from the first few rows of the stands. Britney was wearing a demure tuxedo-style shirt, pants and black heels, Britney sang along with Madge on her third song, "Human Nature," during the show that was three hours late in starting! Timberlake was dressed in black pants, a black jacket and scarf, hot!

A source said "This was a night for [Britney] to enjoy, and not stress over. This was a good moment for her to just enjoy and have fun." And she really enjoyed. Madonna greeted her with "Hi Britney!" And Spears, with her blond hair flowing and red lips smiling, moved to the beat as she sang the last chorus on "Human Nature" with Madonna. Once Madonna started "4 Minutes", Spears was soon out of the view and then Justin joined Madonna later to belt out a full rendition of their duet "4 Minutes." The crowd loved that. "It was great!" a fan told PEOPLE at the show. "They really kept each other going up there. And, wow, only Madonna could bring the two exes together!"

Watch Madonna and Britney performing together.