The 46-year-old was on stage with her bandmates Emma Bunton, Mel B (Melanie Brown) and Mel C (Melanie C) during their final reunion show at London's Wembley Stadium on Saturday, June 15, when she made the emotional announcement.
"I need to say something I should have said a long time ago," Geri shared, as her bandmates put their arms around her. "I'm sorry. I'm sorry I left. I was just being a brat. It is so good to be back with the girls that I love."
Geri's speech, just before the girl group sang "Goodbye", the single that addressed her departure from the Spice Girls, was met with huge cheers from the massive audience.
It wasn't the only emotional moment of the show either. The girls brought their mothers and children out on stage for their performance of "Mama", before Emma broke down in tears during "Viva Forever".
"I've got an ugly cry, haven't I?" she told the crowd. "It's the last night. We're all very emotional."