Nicole, who shot to fame in the group in the 1990s alongside her sister Natalie and Brits Shaznay Lewis and Melanie Blatt, married the former Oasis frontman in 2008 but they divorced in 2014 after 14 years together.
The split was sparked by the news that Gallagher had fathered a lovechild with a U.S. journalist, and now Natalie and her All Saints bandmates have revealed they tapped into the scandal when penning their comeback song, One Strike.
Shaznay says, "When I write, I just think about what's on my mind. The lyrics came from somewhere very real. Nic was going through a lot of things at that time. That was at the forefront of my mind because it was the heaviest thing going on."
Nicole adds, "We spoke for hours and hours on the phone. The first few times I heard it in my car, I couldn't stop crying because I could hear so clearly what it was about."
One Strike is scheduled for release next month (Feb16) ahead of a new All Saints album, Red Flag, which is due in April (16).
It marks the band's first new album in 10 years, since 2006's Studio 1, and main songwriter Shaznay has revealed she has so many tracks left over from the sessions that they are already eyeing a follow-up record.
She adds, "Seriously, I got on such a roll writing and recording with the girls again, we've started getting material for the next album together already. This couldn't feel any more right."