Ginger Spice’s reluctance to participate was reportedly putting the other members – Posh, Mel B, Mel C and Baby – in a position where they risked losing control over the series.
“Netflix are the organisation who defied the wishes of real royalty and went and made The Crown, so they aren’t afraid to go it alone when they have to.”
The group previously used the rule of four in 2019 when Victoria Beckham was too busy with her fashion commitments to join their reunion tour.
They stand to receive about £1 million ($2.3m) for the series.
Rumours of tensions in the band have circulated since Horner left in 1998, remarking in the documentary Giving You Everything she “felt she didn’t belong any more”.
More recently there were rumours of a feud in 2019 after Melanie Brown, otherwise known as Scary Spice, told Piers Morgan she and Ginger had once slept together.
Horner, formerly known as Geri Halliwell, is married to Christian Horner, the former team principal of Formula 1 team Red Bull.
He was embroiled in a sexting scandal last year when it was revealed he was being investigated for misconduct towards a female colleague.
After Red Bull cleared Christian Horner of the allegations, inappropriate messages between himself and the woman were leaked.