The 44-year-old singer has revealed she quit the girl group to give the others ''space'' as she felt she couldn't fully back a R&B album.
She said: ''Sometimes you have to give people space. Like they went off to make a third album, which I think was very authentic to them. They had to make that R&B album, which I'm not ...
''I don't know how to write R&B music, I really don't. I don't have that. So they did that album and made a very good album, with Rodney Jerkins at the top of his game. It had to be done and that's quite right, as an artist you want to explore.''
And the 'Wannabe' hitmaker enjoyed reuniting with Mel B and Emma Bunton in the studio and whilst she would ''welcome'' a reunion at any time, she insists the trio were just ''experimenting'' and there are no plans to come together again for the moment at least.
She added: ''We were experimenting - I absolutely adore the girls and would welcome to share that stage space with them at any point and at any time.
''When I saw Liam Gallagher the other day I suddenly understood it - when Liam was up on the stage and I wanted Noel to be with him. People like it when people come together. They like the relationship, the magic. I remember when I was going on with the Spice Girls on the Olympics. I said we've got four and a half minutes to unify the world. That's it.''
Geri - who has 11-year-old daughter Bluebell from a previous relationship and five-month-old son Montague with her husband Christian Horner - sees her Spice Girl bandmates like university friends.
Speaking to Dan Wooton for his Bizarre Life podcast, she said: ''I would say it's like family members or people you went to university with. You've got that strong connection - it doesn't matter whether you haven't seen them for a bit, you go instantly to honesty, instantly to say it how it is.
''For me, the Spice Girls has always belonged to everyone. You know, of course we wanted to have success - but actually, Bob Dylan said this isn't an album, this is a movement, and it was.''
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