Britney Spears was left emotional when an old friend auditioned for The X Factor on Sunday.

The "Toxic" hitmaker was visibly moved when the man - whose identity has not been revealed - took to the stage at San Francisco's Oracle Arena but remained "calm and supportive" when he confessed to her that he is gay.

As the man stepped out, Britney exclaimed, "I know him. We did a duet together 10 years ago."

"You could see that Britney recognized him straight away. She got this huge smile on her face and her eyes lit up. It was so sweet," an onlooker said.

The hopeful than began to cry and confessed to the audience "I'm gay," before turning to address Britney. "At the time I didn't think I was worthy. I didn't think you thought it was OK that I am gay," he said.

"I think it is fine you are gay," the singer replied.

Britney was described as being "visibly shaken" by the auditionee, but impressed with the way she handled the situation. "When he started crying and saying he thought he'd never see her again and that he'd had a lot to deal with, Britney was comforting him to calm him. She's been through a lot in those 10 years, too, so it must have been a shock for her to see him. You could tell she was emotional and she really felt for him especially when he was crying, but she also stayed calm. She handled it unbelievably well and really stepped up to the situation. It was probably the most personal and emotional situation for her that's happened so far on X Factor, and she took it totally in stride in front of a live audience of thousands," a source said.

The insider refused to say whether the man made it through to the next round of the audition process.

Meanwhile, it has been confirmed that The X Factor will return to the small screen on September 12, with the second episode airing a day later.