The 43-year-old singer is set to reunite with the 'Wannabe' hitmakers for a special tour in just a few weeks time, and has revealed that during her original run with the girl group over 20 years ago, she had ''one time'' fling with Geri, which she insists will never ''happen again''.
She said: ''We were best friends. It just happened. It wasn't a thing. It just happened. We just giggled at it and that was it. It just happens one time and then you talk about it and it does not really happen again. It was just that one time.''
But Mel fears 46-year-old Geri - who is now married to Christian Horner - won't be too happy with her decision to come clean about the romp.
She added: ''Hopefully when Geri gets asked she wont deny it, because it was just a thing. It was not anything major. It was just a fun thing. You asked me a question and I answered it.
''She is going to hate me for this because she is all posh in her country house and her husband. But its' a fact. She is going to kill me and so is her husband.''
And although she only had a sexual encounter with Geri, Mel insists she kissed ''all'' the other group members, made up of Mel C, Emma Bunton, and Victoria Beckham.
Speaking to Piers Morgan in a promotional clip for his ITV chat show 'Life Stories', she said: ''When I got my tongue pierced we all kissed. But that was just a kiss because I wanted to know what it felt like. It was just a silly kiss. Nothing sexual like that.''
Mel's full 'Life Stories' episode is set to air in the UK on ITV this summer.
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