The Absolutely Fabulous star was enjoying a meal with her comedy sidekick Dawn French in the early 1990s when the five budding pop stars approached them.
The girls excitedly told Saunders they were about to hit the big time, but she dismissed their optimism and was left red-faced months later when she saw the band on TV performing debut hit, Wannabe.
Saunders, who is currently promoting her Spice Girls-inspired West End musical Viva Forever!, tells U.K. talk show host Graham Norton, "I actually met them before they were famous. I was in a restaurant with Dawn and in came these five overexcited little girls with braided hair - they came bounding over to us saying, 'Oh my God, French and Saunders,' and told us they were going to be the next big girl group. I thought 'Please, of course you are!' and then suddenly they were on TV and I thought, 'Doh!"