The X Factor judge, 39, shot to fame in 1996 with the band, alongside Victoria Beckham, Emma Bunton, Geri Halliwell and Mel C, and went on to sell over 80 million records with them.
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Although they managed huge success – eventually becoming the biggest selling girl group in history – Mel revealed that they used to fight constantly.
Appearing on Larry King's US chat show, she said: "We fought like cats and dogs. You've got five women together."
Mum-of-three Mel also confessed that she, Melanie C, Victoria and Emma are unsure about how old Geri really is.
When the group first launched, Geri claimed she was 21 but it was later revealed that she was actually 25. After Geri 'celebrated her 29th birthday a few years running', Victoria slipped up and revealed she had in fact already turned 30.
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Mel continued: "We still don't know how old Geri is, to this day. But she's the oldest and Emma was the youngest and me, Victoria and Mel C were all kind of in-between. So we were all quite close together in age.
"But we were like family, we were like sisters, where one would not get on with the other one and another one would kind of make peace and create a nice environment."
On their split in 2000, Mel said: "We didn't really break up. We had like a five-year plan – that kind of got shortened after three years – that we were all eventually going to go our own way.
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"We knew that this was a platform. We always knew that Victoria would go into fashion, Mel C was always going to do music, Emma wanted to do radio, I kind of wanted to do a bit of everything so we had that understanding. But it did come early."
After a seven-year hiatus the Spice Girls reunited for a tour and greatest hits album in 2007, before coming back together again in 2012 to perform at the Olympics closing ceremony in London.