Geri Halliwell has let slip the group's comeback single will be a ballad called 'Headlines', she said the band reforming was like being given a second chance.
She also compared the Spice Girls' reunion to friends who were now a little older and wiser getting back together and realising school was better than they remembered.
The original Ginger Spice, 35, only hinted at past rifts between the five members of the group when she conceded it was difficult to balance work with friendship.
And she described their tour selling out in just 38 seconds earlier this week as "shocking", but promised fans they would have a night to remember at the shows later this year.
She told GMTV: "It is different. The only way I can describe it is like when you look back on your school days. When you are at school, sometimes you think 'oh God' but you look back and think actually, that was so much fun, it was a laugh with your schoolmates.
"It's getting to revisit something, a little bit older, a little bit wiser."
She added: "It's so amazing. It is like waking up and you get a second chance to be something that is so enjoyable."
Of their sell-out tour, she said: "It is kind of shocking. 38 seconds, it's pretty amazing. I cannot quite believe it."
Halliwell, who is now a mother of one, also revealed that the new single, which she described as "absolutely amazing", was finished.
She said: "Emma and I initially worked on it with the original writers we used to collaborate with and then the other girls chipped in later on, adding lyrics.
"Its a Spice Girl classic. We are so proud of it. We started putting words down before we even had the finalised yes from everyone.
"It was kind of like a prayer - when you kind of put the footwork in hoping that it will happen - so it is a really special song, it's kind of magical... It's a big love song."
The group's worldwide comeback tour, which starts in Canada on December 2, will be the first time the group have appeared as a five since Halliwell left the band in 1998.
She said today that it was hard to "juggle that balance" between work and friendship, saying: "It's fantastic hanging with girls you really like but there are pressures of work to go with it so it's about finding that balance. It's like planning a wedding..."
Like Halliwell, Melanie Brown, Victoria Beckham and Emma Bunton are now all mothers and she said this had "really bonded" the group.
She said: "It is such a gift to be a mother. I understand what the others go through because it's hard. It's amazing, the love you feel for your child."
Fans will be given a second chance to get their hands on tickets for the tour when phone lines are opened up tomorrow for two new dates added to the London leg.
Halliwell promised: "It is going to be amazing. It's going to be like a piece of theatre. It has got a story to it. It is really creative."
And she scotched the idea that it will make the group a fortune, saying: "People think you are going to be loaded but you have to do about 99 dates to break even by the time you have paid for the huge screen and all of those things.
"This reunion is about the fans and us celebrating the past. It's more about that."
The new Spice Girls album is out on November 12 and the single will be released a week later.
